

m\ 






Class j Q p 3 3 
Book Ml 
Copyright^! 

COPTOIGHT DEPOSIT. 



PHYSIOLOGY OF MAN 
AND OTHER ANIMALS 



BY 

ANNE MOORE 

A.B., A.M. (Vassar); Ph.D. (University of Chicago) 




NEW YORK 

HENRY HOLT AND* COMPANY 

1909 






-s?' 



Copyright, 1909, 

BY 

HENRY HOLT AND COMPANY 



>CU25.154;4 



TO 

THE CLASS I MOST 
ENJOYED TEACHING 



PEEFACE 

No new facts are presented in this book. Rather has 
an attempt been made to present simply from a physio- 
logical standpoint the well-established facts of physiol- 
ogy. To this end all details that might complicate the 
matter have been omitted and a few general principles 
have been emphasized. 

Human physiology is frequently presented in our 
schools as an isolated subject unaffected by the laws of 
other sciences. For this reason it fails to produce an 
improvement in personal hygiene, and it fails to provide 
mental discipline. To the young student then the 
human body is apt to seem a unique development, its 
structure and its functions unwarrantably complex and 
its behavior quite independent of the ordinary laws 
of nature. 

For four years in one of the best normal schools, the 
author struggled with this mental attitude in pupils com- 
ing from the lower schools. They seemed to have no 
conception of cause and effect in connection with the 
human body. The one idea most prevalent among them, 
most antagonistic to the understanding of the principles 
of hygiene and ; hysiology and most difficult to eradicate, 
was the idea that things happen because the body needs 
them to happen. That the operation of definite phys- 
ical and chemical laws might have an effect upon the 



vi PKEFACE 

body seemed beyond their grasp. They had no diffi- 
culty in understanding that the ameba gets oxygen be- 
cause a gas passes in a definite direction, for the ameba 
was unfamiliar and a new idea could be easily and 
quickly gained concerning it; but almost simultane- 
ously they would assert that a human being gets oxygen, 
even in a vitiated atmosphere, because his system needs 
oxygen. Their minds stopped working logically as 
soon as human physiology, the familiar thing, was in 
question. 

Until the simple fact that natural laws act upon all 
organisms alike is grasped there can be no intelligent 
comprehension of physiology and no intelligent applica- 
tion of its laws to the health of the body. This fact is 
the keynote of its rational presentation, and it should 
be emphasized from the beginning, for if a correct gen- 
eral impression is established, it may serve as a basis 
upon which it is possible to build without first tearing 
down and re-establishing the foundation. 

The course suggested in this book can be covered by 
the work of a year. It divides itself naturally into two 
parts. In the first part certain general principles are 
defined and are shown to govern the functions of organ- 
isms. In the second part modifications of these func- 
tions resulting from structural development are con- 
sidered in representatives of the great groups of 
animals. 

It frequently happens that a teacher must make her 
pupils conversant with a certain phase of a subject when 
she knows that it will be better for them to have some 
other phase of it emphasized. By following some such 



PREFACE vii 

plan as the one indicated she may stick to the letter of 
the law and at the same time follow the spirit of her 
better judgment, laying, in each individual case, the 
stress where it is most needed. 

This book has been written with the conviction that 
the development of a pupil's mind is more important 
than the accumulation of facts and with the conviction 
that physiology may be made to contribute to this mental 
development by the appeal which it makes to the reason- 
ing power. Children like to reason, and a sympathetic 
teacher, interested in the subject, and prepared to teach 
it, can, by appealing to the reasoning faculty, change the 
study of physiology from a perfunctory compliance with 
the law to a real pleasure. 

The manuscript has been read by Miss A. St. L. 
Eberle, to whom I am much indebted for criticism and 
suggestion. I am further indebted to Messrs. Henry 
Holt and Company for much courteous consideration, 
and for permission to use illustrations from some of 
their publications; especially am I indebted for the 
use of those from " A General Biology " by Sedgwick 
and Wilson; " Principles of Physiology and Hygiene " 
by Dr. George Wells Fitz ; " The Human Body " by H. 
Newell Martin; and " A Manual of Zoology " by Rich- 
ard Hertwig. 



CONTENTS 
PART I 

INTRODUCTION 

CHAPTER I 

LIVING MATTER 

PAGE 

Organisms composed of living substance — Appearance of liv- 
ing substance — Meaning of the word cell — Importance 
of the cell — Irritability — Assimilation — Reproduction — 
Universal characteristics — Non-living matter in a living 
cell — Starch in the potato — Starch used for food — A 
question simplified — Matter — Heat — Diffusion — Osmosis — 
The question answered — Chemical action — Combustion 
— Characteristics of hydrogen, carbon dioxide, oxygen — 
Heat and chemical action — Manufacture of starch — 
Transfer of starch — Purification of air — Air, its compo- 
sition and pressure — Summary 7 

CHAPTER II 

RESPIRATION 

A universal process — The process defined — Necessary condi- 
tions — The law of gases — Passage of a gas through a 
membrane — Influence of pressure on rate of passage — 
Establishment of an equilibrium — Independent behavior 
of gases — Application to respiration — Free oxygen — 
Equilibrium of nitrogen — Respiration in specific animals 
— Lower animals — Higher animals — Respiratory organs 
in aquatic animals — Relation between the blood and the 
gill membrane — Situation of the moist membrane — Re- 
spiratory organs in land animals — Mechanism for bringing 

ix 



x CONTENTS 

PAGE 

air in contact with the membrane — Respiratory muscles 
— Inspiration — Expiration — Effect of the elasticity of the 
lungs on the diaphragm — Phraseology — Hygiene of res- 
piration — Summary 23 

CHAPTER III 

ASSIMILATION 

Steps in the process — Nature of the process — In one-celled 
animals — In many-celled animals — The complete digestive 
tract — Variations in development — Diet of animals — The 
five food substances — Water — Salts — Carbohydrates — Hy- 
dro-carbons — Proteids — Necessary proportions of food sub- 
stances — Nutriment in foodstuffs — Digestion — Enzymes 
— Enzymes in the digestive juices — Reversible action of 
enzymes — Enzymes in the tissues — Passage of food 
through the canal — Absorption in the intestine — Excre- 
tory organs — The kidneys — Urea — The sweat glands — 
Hygiene of digestion — Summary 45 

CHAPTER IV 

CIRCULATION 

Necessity for circulation — The system — In lower animals — 
In higher animals — Mechanical factors which control the 
circulation, 1 ) The heart, 2 ) The valves, 3 ) The closed 
system, 4) Elasticity, 5) Tone — Composition of the 
blood — The red corpuscles — Relation between ogyxen and 
hemoglobin — Oxygen can not establish an equilibrium — 
Origin and fate of the corpuscles — The white corpus- 
cles — Coagulation — The serum — The lymph — The lym- 
phatics — Vaso-motor nerves — Relation to the body tem- 
perature — Interference with the vaso-motor mechanism 
— Effect of alcohol on body temperature — Adaptation of 
the circulation to bodily need — Summary 67 

CHAPTER V 

EEPEODUCTION 

Origin of living matter unexplained — Reproduction — In one- 
celled animals — In many-celled animals — Restricted to 



CONTENTS xi 

PACK 

Bpecial oells — Reproductive cells of the sea-urchin — At- 
traction of the sexual cells — Division of the fertilized egg 
— Differentiation of cells — The process universal — Pro- 
tection of the cells in hunt animals — Sexual reproduction 

of plants — Summary 87 

CHAPTER VI 

IRRITABILITY 

Protoplasmic motion — Ciliary motion — Muscular contraction 
— Theory of muscular contraction — Stimuli — Rhythmical 
contraction — Influence of the structure of muscles — In- 
fluence of arrangement of muscles — The function of a 
skeleton — The skeleton external in lower animals — In- 
ternal in higher animals — The structure of bones — The 
spinal column — The shoulder girdle — The pelvic girdle — 
The ribs — Appendages — Joints — Relation of muscles to 
bones — Relation of nerves to muscles — Structure of the 
nervous system — The work of nerves — The value of the 
nerves — Sense organs — Sympathetic system — Exercise — 
Effect of alcohol on the nervous system — Summary 99 



PART II 

INTRODUCTION 

CHAPTER VII 

PROTOZOA 

Habitat — The ameba — More highly specialized forms — Food 
substances — Wastes — Respiration — Reproduction — S u m - 
mary 128 

CHAPTER VIII 

CCELENTERATA 

Many-celled animals — The primary layers — Tissues of the 
coelenterata — Distinguishing characteristics — Assimila- 



xii CONTENTS 

PAGE 

tion — Irritability — Fixed forms — Nervous system — Colo- 
nial forms — Reproduction — Alternation of generations — 
Summary 135 

CHAPTER IX 

ECHINODERMATA 

Characteristics — T h e starfish — Symmetry — Internal struc- 
ture — Irritability — Mechanics of locomotion — Assimila- 
tion — Reproduction — Regeneration — Summary 147 

CHAPTER X 

MOLLUSCA 

Shells — The living animal — Formation of the shell — The Clam 
— Gills — Circulatory system — Alimentary canal — Nervous 
system — Economic value — Characteristics of the group.. 154 

CHAPTER XI 

VERMES 

Irritability of the earthworm — Mechanics of locomotion — 
Surface characteristics — Assimilation — Increase of diges- 
tive surface — Circulatory system — A segment — Excretory 
organs — The nervous system — Reproduction — Classifica- 
tion — Flat worms — Round worms — Segmented worms — 
Molluscoidea 162 

CHAPTER XII 

ARTHROPODA 

External characteristics — Nervous system — Digestive system 
— Respiratory system — Excretory system — Circulatory 
system — S e n s e organs — Reproduction — Appendages — 
Classification — Crustacea — Locomotion of the lobster — 
External characteristics — Moulting of the shell — Diges- 
tive system — Other organs — Respiration — Reproduction — 
Segmentation — Acerata — Myriapoda — Insecta 173 



CONTENTS xiii 

CHAPTER XIII 

VERTERRATA 

PAGE 

Irritability — Assimilation — Respiration — Reproduction — Gen- 
eral characteristics — Classification 185 

CHAPTER XIV 

PLANTS 

Irritability — Assimilation — Reproduction 189 

Appendix 192 

Review Questions 201 

Index 205 



INTEODUCTION 

Physiology is a study of activity. It deals with the 
activity by which a living plant or animal manifests 
the fact that it is alive, and the activity of the various 
parts of its body which do the work required to keep 
it alive. 

Physiology is related to anatomy in very much the 
same way that the work that a machine is capable of 
doing is related to its structure. When we study the 
anatomy of an animal we study the structure of its body, 
and we may do this through dissection after it has been 
killed. But when we study physiology we study the 
manifestation of life, the curious incomprehensible thing 
which marks the infinite, possibly the infinitesimal, dif- 
ference between inert matter and a sensitive organism. 

It has been customary to devote a large amount of 
space in text-books of human physiology to a considera- 
tion of anatomy. Structure and function have been 
presented together and causal relations have been estab- 
lished between them. This has led to confusion of 
thought. Structure has come to be regarded by young 
students as the underlying cause of function ; and char- 
acteristics common to all animals as peculiar to human 
beings. This is fundamentally wrong. Structure can 
not initiate activity. It can only control or modify it. 
Although the activity of living organisms may be regu- 



2 INTRODUCTION 

latecl by their structure, it is dependent primarily on 
living matter itself. The functions of human beings 
are therefore not unique. They are but highly developed 
characteristics common to all animals. 

We do not tat and breathe because we have a certain 
number of bones and a definite arrangement of muscles, 
though the manner of eating and breathing may be in- 
fluenced by this arrangement. We might as well expect 
a steam engine to go because it has a certain number of 
wheels and pistons. These may determine the manner 
of its going, but without the steam it remains still. A 
dead man has the same gross anatomy as a living man. 
If anatomy were a determining cause of activity the 
functions of the body would not stop when death occurs. 

Exactly what the difference between living and dead 
matter may be we do not know, but we do know the way 
in which living matter manifests the fact that it is alive ; 
and we know that wherever it is found, in the simplest 
animal or in the most complex, these manifestations are 
the same. The point of departure in the study of physi- 
ology should therefore be the activity of the living sub- 
stance. In studying this activity and the causes that 
control it we find that physiology is related to physics 
and chemistry and that this relation is more vital than 
its relation to anatomy. Through physics and chemistry 
we may explain the activity of living matter; through 
anatomy we explain nothing but accidental modifica- 
tions of its activity. 

The human body, though the most complex and won- 
derfully efficient machine in existence, has in common 
with the simplest animals and plants only the functions 



INTRODUCTION 3 

that belong to living matter. Every organism assimi- 
lates food, substances circulate through all parts of its 
body, it breathes, it moves and it is able to produce its 
kind. These are the functions that we are to study. To 
explain their simple universal features we must have re- 
course to the principles of physics and chemistry. No 
adequate explanation can be made of any process with- 
out a knowledge of these principles, for in all purely 
physical operations the animal obeys certain natural 
laws, usually without knowledge on its part, of what it 
is doing and certainly without volition. But as the pecu- 
liar way in which the functions manifest themselves is 
dependent upon structure, to explain the manner of their 
occurrence in any particular animal we must have re- 
course to anatomy. 



PAET I 



CHAPTER I 

LIVING MATTER 

Organisms Composed of Living Substance. — Every 
organism is composed mainly of living substance. Its 
characteristics, functions and powers are dependent on 
the nature of the living substance. If then we are to un- 
derstand the physiology of any plant or any animal we 
must know something about this substance. We must 
study it, not in its most highly developed form, as it ap- 
pears, for instance, in the muscles and nerves of human 
beings, but in its simplest state. We shall then find out 
what the characteristics are that distinguish it from 
everything else. These characteristics are few and 
always the same. They may become more complex 
as the result of some special development, but no 
matter how highly developed this substance may be, 
it can not take on new powers, it can only develop and 
modify those that belong to it simply because it is alive. 

Appearance of Living Substance. — If we scrape a few 
hairs from the stamen of such a flower as the wandering 
jew and examine them with a compound microscope we 
can see what this substance looks like. Each hair is 
made up of a series of compartments which appear more 
or less transparent (Fig. 1, A). Within the trans- 
parent space in each compartment a shadowy, granular 

7 



PHYSIOLOGY 



H 



w 



u 



w 



M 



U 







if fcMM 



mmmwmM 



Fig. 1.— -4, a hair from the stamens of spiderwort ; i?, a single cell enlarged. The 
circulation of the protoplasm is indicated by the arrows; n, nucleus. (From 
Sedgwick and Wilson.) 

substance slowly streams about (Fig. 1, B). This granu- 
lar substance is the living substance, or protoplasm, 
as it is usually called. The most remarkable thing that 
we notice about it, is- that it moves apparently without 



LIVING MATTEE 9 

anything to make it move. The streams of protoplasm 
seem to flow from a spot of thickened protoplasm called 
the nucleus. This spot is always a center of activity. 
The transparent space around the protoplasm is called 
the vacuole; the enclosing wall, the cell-wall; and the 
entire structure, the cell. 

Meaning of the word Cell. — The name cell was given 
to the structure when microscopes were very poor. In- 
vestigators saw only the w r alls and attached undue im- 
portance to them. The name now refers not to the 
walls but to the living substance which w 7 e know to 
be infinitely more important. A cell is a little mass 
of protoplasm which contains a nucleus. It may, or 
may not, be surrounded by a definite wall, and it may, 
or may not, contain other things. 

Importance of the Cell. — A simple cell, or protoplasm 
in its simplest form, is the starting point of every plant 
and every animal. Some plants and animals never get 
beyond the starting point ; that is, they remain all their 
lives in the one-celled stage. Such single cells are able 
to do everything necessary to the life of an independent 
organism. By studying these one-celled forms, then, it 
is possible to discover the wonderful powers that charac- 
terize living substance and all living organisms. 

Irritability. — If a drop of stagnant water is placed on 
a glass slide and examined with a compound microscope, 
minute, one-celled, transparent animals may be seen 
moving swiftly across the field. If one of them is quiet 
long enough, we may see in its body what we have 
already seen in the hair cell. The protoplasm is mov- 
ing. But as we look, the animal scurries away. 



10 



PHYSIOLOGY 




This independent movement from place to place is 
merely a mechanical response to some form of motion 
within the cell. On the surface of 
some of these animals are tiny, hair- 
like projections called cilia (Fig. 2). 
The protoplasm inside moves in such 
a way that the cilia wave to and fro ; 
the animal then moves through the 
water like a boat propelled by oars. 
Still others have a tail-like projection 
which becomes fastened to something 
in the water (Fig. 3). Within the 
tail is a thread of protoplasm at- 
tached alternately first on one side 

Fig. 2. — Paramecium 

showing cilia. (From and then on the other. Ihis thread 
McMurrich.) contracts and the animal is pulled 

away from anything that may happen 

to touch it. Movement in response 

to an outside stimulus, or irritation, 

is called irritability. 

Assimilation. — Another thing that 

attracts the attention as we watch 

these animals in the drop of water, is 

that some are larger than others of 

the same kind, just as cats are larger 

than kittens, and men are larger than 

boys. We may infer from this dif- 
ference in size that they have the 

power of growth, or the .power to 

add new protoplasm to their bodies, and that in order to 

get the materials for the manufacture of protoplasm, 




Fig. 3.— Vorticella 
showing stalk of con- 
tractile protoplasm. 
(From McMurrich.) 



LIVING MATTEE 11 

they must take in fond. [f we watch patiently we 

may see them eat. They do this in a primitive way. 
They simply engulf another organism smaller than them- 
selves. The parts of this organism which are unfit for 
the building up of new protoplasm they eject from their 
bodies. The nutritious material they retain and manu- 
facture into protoplasm. This process is called assimi- 
lation. 

Reproduction. — If we continue to watch, we may 
notice that when one of these animals has attained its 
full growth it splits into two small ones. (Fig. 4). 



■&$&&'" ••'■ - — " S ' - vK*W II I 

jNtir ] ^§mh fy 

\ e o c - / v, ° ■• y 

*-^v ';>' " 

Fig. 4.— Ameba dividing by fission. (From Sedgwick and Wilson, after Leidy.) 

Each of these assimilates food, grows to maturity and in 
turn divides. The number of animals is thus rapidly 
increased. This is the simplest form of reproduction. 

Universal Characteristics. — Irritability, assimila- 
tion, and reproduction are universal characteristics of 
living matter and of all organisms composed of it. The 
study then of any organism means the study of the spe- 
cific way in which these characteristics manifest them- 
selves. 

Non-Living Matter in a Living Cell. — Suppose we 
look at a cell which differs from those we have seen in 




12 



PHYSIOLOGY 




Fig. 5.— A section of potato showing starch 
grains within the cells. 



that it contains other substances besides the living sub- 
stance. Such a cell may be obtained by cutting a very 
thin section of a potato. (Fig. 5). When we look at 

the section with the 
compound microscope 
we see two things ; the 
walls of a series of ir- 
regular boxes, and en- 
closed by them a great 
many transparent glob- 
ules. 

Starch in the Potato. 
— What are these glob- 
ules ? Doubtless in the 
beginning chemists tried many tests before they found 
out, but now that we know the test to apply, it is 
a very simple matter to prove that the globules are 
made of starch. Iodine stains brown whatever it 
touches except starch and this it stains blue. We may 
test this by putting a few drops on a lump of starch and 
on something which we know contains no starch. If we 
put a drop of iodine on the potato cell the protoplasm and 
the cell walls turn brown and the globules turn blue. 
The globules are therefore made of starch. After this 
we will refer to them as starch grains. 

Starch Used for Food. — What are the starch grains 
in the potato for ? The starch is made and stored for 
the sake of furnishing the living substance of the potato 
with something with which it can repair wear and tear. 
It is one of the substances out of which new protoplasm 
is made.- 



LIVING HATTER 13 

A Question Simplified. — If we understand how the 
starch grains are made and how they get into the cells 
of the potato it will simplify the attempt to explain 
similar processes in the human body. Starch is manu- 
factured inside the plant of water and carbon dioxide. 
The water enters the plant through its roots, the carbon 
dioxide through its leaves. How? We may consider 
the root and the leaf as more or less hollow structures 
covered with a thin, moist membrane. The membrane 
is a solid, the water is a liquid, and the carbon dioxide 
is a gas. How do a gas and a liquid pass through a 
solid ? In order to explain this, we must know some- 
thing about the nature of a gas, a liquid, and a solid. 

Matter. — Every substance, everything in the world 
that can be called matter, is made of very tiny particles. 
These little particles are constantly rotating, or vibrat- 
ing very rapidly, and they have more or less power to 
move away from each other. 

If they move very slightly so that they do not change 
their relative positions, the substance has a definite 
shape and a definite volume and we call it a solid. If 
they move freely but not entirely away from each other 
the substance has a definite volume but no definite shape 
and we call it a liquid. If their motion is unrestricted 
so that they may fly entirely away from each other the 
substance has neither definite shape nor definite volume 
and we call it a gas. 

Heat. — The word heat means rapidity of vibration. 
In response to heat a substance may change from a solid 
to a liquid, or from a liquid to a gas. As it grows hot its 
particles move more rapidly and push farther and 



14 PHYSIOLOGY 

farther apart. They do not change in size or in number 
but the spaces between them become larger and the sub- 
stance occupies more space than it did before. (Fig. 6). 

A B 



Fig. 6.— A diagram illustrating expansion. A bit of matter, A, before ; B, after 
the application of heat. The particles have not changed, but as they are far- 
ther apart they occupy more space. 

When butter melts, it expands until it becomes a liquid. 
When water evaporates, it expands until it becomes a 
gas. In both cases the increased motion of the particles 
represents an increase in heat, and the increase is the 
same whether the process takes place quickly or slowly. 
The increase of heat, or motion, on the part of one sub- 
stance means a corresponding loss of heat, or motion, on 
the part of some other substance, thus there can be no 
evaporation unless something is cooled in the process. 
If a hot substance is brought in contact with a cold sub- 
stance, the more rapidly moving particles transfer their 
motion to the more slowly moving ones as a bat does to 
a ball, and as the one substance grows warmer the other 
grows colder until the temperature of both is the same. 
If a substance evaporates from the surface of the body, 
it takes heat from the body in so doing and we feel 
cooler. 

Diffusion. — Water apparently disappears when it 



LIVING MATTER 



15 



evaporates. When 1 does it go? As it becomes a gas, the 
particles on the surface move away from their fellows 
and pass into the nearest space that is open to receive 
them. If the water is in contact with air, this space is 
between the particles of the air. (Fig. 7, A). The air 



B 



Fig. 7.— A diagram illustrating diffusion. Two substances in contact, A, before; 
B, after diffusion has begun. 

particles are also moving rapidly and they pass into the 
spaces between the particles of the water. (Fig. 7, B). 
The particles of each substance then continue to move 
from space to space in the other until each holds as much 
of the other as it can, or until one of them is entirely 
taken up by the other. This process is called diffusion. 

Osmosis. — If the water were separated from the air 
by a moist membrane, diffusion would take place 
through the membrane. As the membrane is a solid, its 
particles do not move away from each other, but through 
the spaces between them the particles of air and of water 
pass to the other side and the two substances become in- 
termingled. (Fig. 8). This process is called osmosis. 

The Question Answered. — Through the process of 
osmosis a liquid or a gas can pass through such a solid 



16 PHYSIOLOGY 

as a moist membrane. A cell-wall is a moist membrane. 
If the particles of a liquid or a gas come in contact with 
it they pass into the spaces between the particles of the 

A B 



Fig. 8.— A diagram illustrating osmosis. Two substances separated by a mem- 
brane, A, before ; B, after osmosis has begun. 

cell-wall and get through to the other side. In this way 
water and carbon dioxide pass into the root and leaf, 
starch into the potato cell, and substances pass from cell 
to cell in the bodies of organisms. 

Chemical Action. — How are starch grains made? 
Water and carbon dioxide enter the plant by a physical 
process which involves no change in their nature. In 
the plant they are manufactured into starch, an abso- 
lutely different substance. This is done by a chemical 
process. In chemical action two or more simple sub- 
stances unite to form a complex substance, or a complex 
substance splits into the simple substances of which it is 
composed. 

Combustion. — Carbon dioxide is a colorless gas, and 
as its name indicates it is made of two substances, car- 
bon and oxygen. Oxygen is a colorless gas and as far as 
appearance goes it is not to be distinguished from carbon 



LIVING MATTER 17 

dioxide. Carbon is a black solid best known in the form 
of charcoal. 

When oxygen unites with a substance, the substance 
is said to burn. When wood burns oxygen from the air 
unites with two substances in the wood, carbon and 
hydrogen, a colorless gas. The union of oxygen with 
carbon produces carbon dioxide; with hydrogen, water. 
The substances in wood that do not unite with oxygen 
are left unburned in the form of ashes. 

When a substance burns its weight is increased by the 
weight of the oxygen that unites with it. It may be hard 
to realize that an invisible gas has weight and that a 
thing weighs more after it is burned than before, but the 
fact is easily proved. When magnesium wire is burned, 
the resulting product is a white powder called magne- 
sium oxide. The weight of the powder is greater than 
that of the original piece of wire by the amount of oxy- 
gen which has united with it. 

Characteristics of Hydrogen, Carbon Dioxide, Oxy- 
gen. — If a burning splinter is thrust successively into 
three jars containing hydrogen, carbon dioxide and oxy- 
gen its behavior in the three cases is markedly different. 
In the jar of hydrogen, it goes out, but the hydrogen 
itself begins to burn at the mouth of the jar with a blue 
flame. The heat of the burning splinter raises the 
hydrogen to the kindling temperature and it unites with 
oxygen from the air. The water that is formed appears 
in drops on the side of the jar. 

In the jar of oxygen the splinter burns for a moment 
much more freely than it does in the air; then it goes 
out. In the carbon dioxide, it instantly goes out. 



18 PHYSIOLOGY 

If a small amount of clear lime water, which is a test 
for carbon dioxide, is now put into these two jars, it 
turns milky in both, showing that in the one case oxygen 
united with carbon from the splinter to form carbon 
dioxide, and that in the other the carbon dioxide was 
unchanged. Carbon dioxide does not burn because it 
can not hold any more oxygen; it does not allow any- 
thing to burn in it because it will not allow the oxygen 
w T hich it holds to unite with anything else. It is there- 
fore inactive. 

Oxygen is very active. It burns, or unites with, al- 
most everything with which it comes in contact if the 
temperature is raised to the kindling point. Even iron 
burns in it, forming iron oxide or rust. 

Heat and Chemical Action. — There is a very close 
relation between heat and chemical action. We use a 
burning match to light the fire because heat is necessary 
to bring about chemical action, and we sit near the fire to 
get warm because chemical action gives rise to an in- 
crease in heat. Heat, then, becomes an evidence that 
a chemical action which may be invisible is taking 
place. Heat will be given off whether the action takes 
place quickly or slowly, but if the action takes place 
slowly, as in the rotting of wood, or in the rusting of 
iron, it is not evident to the senses. 

Manufacture of Starch. — When starch is made, six 
parts of carbon dioxide and six parts of water unite 
chemically to form one part of starch. Twelve parts of 
oxygen are left over. (6CO 2 +6H 2 O=C 6 H 12 O 6 +120). 
The process takes place in the leaf in the presence 
of sunlight, through the activity of chlorophyll^ the sub- 



LIVI.NC MATTER 



10 



r~\ 



stance which gives plants their greeD color. If green 
water plants are placed in a jar of water in the sunlight, 
hubbies of gas may be seen passing away from them. If 
this gas is caught in a test tube and touched with a 
lighted splinter Its behavior proves at once that it is 
oxygen. Its presence is a 
sign that the plant is rapidly 
making starch. (Fig. 9). 

Transfer of Starch. — As 
starch is a solid that does not 
dissolve in water it cannot 
pass out of the leaf where it 
is made until it is changed to 
a soluble form. Through the 
activity of certain complex 
substances (see enzymes) 
which w T ill be described later 
it becomes converted into 
sugar. In this form it passes 
into the sap, which carries it 
throughout the plant. When 
the sugar reaches the potato 
the complex substances re- 
verse their action and turn 
the sugar into starch, in 
which form it is stored for 
future use. Though there is an obvious advantage to 
the plant in this transformation it takes place not for 
this reason but as a result of chemical activity. 

Purification of Air. — The work that plants do in keep- 
ing alive is of inestimable benefit to man. In making 




Fig. 9.— Alga giving off oxygen. 
(After Bailey.) 



20 PHYSIOLOGY 

starch they not only provide him with a large proportion 
of his food, but by taking in carbon dioxide and giving 
off oxygen, they purify the air, so that it is fit for him to 
breathe. 

Air, its Composition and Pressure. — Air is a physical 
mixture, not a chemical compound. When pure, it is 
composed largely of two gases, oxygen and nitrogen, 
with small traces of water vapor and carbon dioxide. 
Besides furnishing gases that living organisms need, it 
affects them in many other ways, chiefly through its 
weight, which is enormous. It presses upon all sides of 
us in every direction with a force of fifteen pounds for 
every square inch of surface. This force represents the 
weight of a column of air with a base of one square inch 
stretching from the earth to the limit of the atmosphere. 
One would think this weight enough to crush a delicate 
little organism, but the external pressure is so nicely ad- 
justed to the pressure within the body that it does no 
harm, and it regulates many functions. In the hair cell 
the streams of protoplasm are separated by large, trans- 
parent spaces which seem empty. They are, however, 
filled with a transparent liquid which by pressing back 
upon the wall with a force of fifteen pounds to the 
square inch neutralizes the air pressure, which would 
otherwise crush out the spaces and prevent their exist- 
ence. This liquid is sap, or water containing dissolved 
substances, one of which is sugar. 

Summary. — Every organism has a definite cellular 
structure, that is, it is made up of one or more cells, or 
little masses of protoplasm, each of which contains a 
nucleus and is surrounded by a cell-wall. It is further 



LIVING MATTER 21 

distinguished by physiological qualities dependent upon 
the peculiar characteristics of the protoplasm, or living 
substance of which it is composed. 

This substance is distinguished from non-living sub- 
stances by three qualities: irritability, or the power to 
move ; assimilation, or the power to use food substances ; 
and reproduction, or the power to form new protoplasm. 
These qualities of living matter are responsible for the 
behavior of organisms as independent beings. 

Living matter responds to a stimulus with some form 
of motion. This motion may take the form of a circula- 
tion within the cell, or of a contraction. If the contrac- 
tions are organized they will result mechanically in a 
movement of the whole, or of some part, of the independ- 
ent organism from place to place. Food substances are 
used by independent organisms in such a way that new 
protoplasm is formed, endowed with the power of 
becoming differentiated into the specific tissues of a spe- 
cific organism. Food that a sheep eats is never trans- 
formed into the muscles of a fish. Reproduction of 
independent organisms involves the formation of a cell 
endowed with the power to become a new individual like 
the parent. 

These functions are controlled by physical and chem- 
ical laws. The most important of these are (1) All 
matter is composed of particles that move and have 
spaces between them. (2) This motion is the equiva- 
lent of heat which may be transferred without loss from 
particle to particle and from substance to substance. 

As the particles move faster they move farther away 
from each other, and the substance occupies a larger 



22 PHYSIOLOGY 

area than before. This expansion may continue until a 
solid becomes a liquid and a liquid becomes a gas. As 
a liquid evaporates its particles get into the spaces 
between the particles of other substances. If this diffu- 
sion takes place through a membrane, the process is 
called osmosis. 

A physical change does not disturb the nature of a 
substance, but in a chemical change new substances are 
formed either by the union of simple into complex, or 
the disintegration of complex into simple substances. 
The oxidation of carbon and hydrogen in the burning of 
wood is similar to the oxidation of those substances in 
the human body ; in both cases carbon dioxide and water 
are formed. The passage of water and carbon dioxide 
through a membrane is typical of the way in which most 
substances pass from cell to cell in the human body. 



CHAPTER II 
RESPIRATION 

A Universal Process. — All living things breathe. A 
fish in the water and a horse on land breathe ; an ameba, 
the simplest animal, and a human being, the most 
complex, breathe ; a tree and a violet, a jelly fish and a 
mushroom, breathe. They do not take in air and give 
it off by means of a movement of the chest cavity, for 
that is a characteristic of human beings and certain 
other vertebrates, and is only an accident connected with 
the process, but nevertheless they breathe. 

The Process Defined. — What do we mean by this 
word breathe ? If w T e study these diverse cases and 
disregard accidental peculiarities and complications that 
result from structure, or from habit of life, we find that 
when an organism breathes two very simple things in- 
variably occur ; oxygen passes into its body, and carbon 
dioxide passes out of it. This double process is called 
breathing or respiration. 

Necessary Conditions. — Oxygen and carbon dioxide 
are gases. Whenever an animal breathes then a gas passes 
into the body and a gas passes out. In order that this 
may occur two obvious conditions must be fulfilled ; first, 
the gases must be present ; second, some means of passage 
must exist. As the simplest animals have the entire 

23 



24 PHYSIOLOGY 

body surface covered with a moist membrane, gases can 
get into, or out of, the body only by passing through the 
membrane. This fact is important because, (1) All 
animals have more or less of the body surface covered 
with a moist membrane; (2) Any gas coming in contact 
with a moist membrane passes through. 

The Law of Gases. — Why should a gas pass through 
a membrane ? When we explain this we shall have ex- 
plained the underlying principle which governs respira- 
tion. A gas always passes in the direction of the least 
pressure. It does this even if it has to pass through a 
membrane. If the pressure of a gas on the outside of a 
membrane is greater than the pressure of the same gas 
on the inside, then that gas must pass from without in ; 
conversely, if the pressure is greater on the inside than 
on the outside, it must pass from within out. The pres- 
sure of carbon dioxide is continually greater on the in- 
side of the body than on the outside ; it must, therefore, 
pass out of the body. The pressure of oxygen is con- 
tinually greater on the outside of the body than on the 
inside ; it must therefore pass into the body. 

Passage of a Gas Through a Membrane. — If a gas 
is in contact with a moist membrane, its particles, mov- 
ing in every direction quite unrestrainedly, hit against 
the membrane. When they hit another particle they re- 
bound, but when they come to a space they pass through 
if the space is large enough. The ease with which a sub- 
stance passes through a membrane, or whether it passes 
through at all, depends on the relative size of its par- 
ticles and of the spaces between the particles in the mem- 
brane. In a membrane the spaces between the particles 



RESPIRATION 



25 



are larger than those in such a solid as "-lass or steel, but 
they are still so tiny that they are invisible and they 
must not be confused with holes. A membrane has no 
" holes " in it. 

Influence of Pressure on Rate of Passage. — A gas 
Avill pass through a membrane slowly or quickly accord- 
ing to the number of particles that hit the membrane in 
any given interval of time, and this depends of course on 
the amount of gas that is present. The greater the 
amount of gas in a given space, the greater will be the 
number of particles that bombard the membrane in a 
unit of time, the number that reach spaces, and the 
number that pass through. This is but another way of 

ABC 






• • 



Fig. 10.— A diagram illustrating the influence of pressure on the passage of gas. 

saying that the pressure of a gas determines the rapidity 
with which it passes through a membrane (Fig. 10). 

Establishment of an Equilibrium. — Suppose (case 1) 
two empty spaces of equal size, A and B, should be 
separated by a membrane, and a gas should be intro- 
duced into A (Fig. 11). Immediately its particles 
would rush through the membrane and begin to fill 
space B. As soon as a particle arrives in B it stands 
a chance of again hitting the membrane and of getting 



26 



PHYSIOLOGY 



back to A, As long as the number of particles is greater 
in A than in B, a greater number from A than B hit the 
membrane in a unit of time, and the passage from A to 
B is more rapid than from B to A (Fig. 12). In course 



A B 



Fig. 11.— Case 1. A gas confined by a membrane. 

of time the number of particles in B equals the number 
in A. The chance of hitting the membrane and of pass- 
ing through is then the same in both spaces (Fig. 13). 
In other words, when the pressure of a gas is greater 

A B 



• *••»!• • • • 
••••••• • • • 

• ••••<• • • ♦ 
e • • • • I 

• ••••!• » • • 



Fig. 12.— Case 1, after an interval. 

on one side of a membrane than on the other, the passage 
takes place in both directions, but from the side of 
greater pressure it overbalances that from the side of 
less pressure until the pressure on the two sides is equal, 
when an equilibrium is established. Equilibrium does 
not mean that passage stops. It means that in any 



EESPIEATION 27 

given interval o{ time the number of particles that pass 
through from one side equals the number that pass 
through from the other. 

Independent Behavior of Gases. — Suppose (case 2) 
two spaces of equal size, A and B ? should be separated 
A B 



Fig. 13.— Case 1: Equilibrium. 



by a membrane, and suppose a gas X should be intro- 
duced into A and a gas Y into B (Fig. 14). Each one 
of these gases would act independently of the other. It 
would act as if the other were not there, as in case 1 ; and 



Fig. 14.— Case 2: Two gases separated by a membrane. 

would establish its own equilibrium (Fig. 15). If the 
two gases should be kept from forming an equilibrium 
by some mechanism that would keep the pressure of X 
always greater in A than in B and the pressure of Y 
always greater in B than in A ? the passage would simply 



28 



PHYSIOLOGY 



continue independently always in excess in the same 
direction for the same gas. If the pressure of X were 
very much greater in A than in B the passage from the 
side of less pressure might be so small that it could 

A B 



Fig. 15.— Case 2: Two gases in equi 



ibrium. 



be ignored in comparison with the passage from the 
other side ; we would then speak of the passage as if it 
were in one direction only. 

Application to Respiration. — Case 2 represents the 
condition in respiration (Fig. 14). Oxygen or X is 
on one side of the membrane and carbon dioxide or Y 
on the other side. Each gas passes through and estab- 
lishes its own equilibrium quite independently of the 
other (Fig. 15). The pressure of oxygen is so much 
greater on the outside of the membrane than on the 
inside that we ignore the small amount that passes 
out, and speak only of the taking in of oxygen ; and the 
pressure of carbon dioxide is so much greater on the 
inside than on the outside that we ignore the small 
amount that passes in and speak only of the giving 
off of carbon dioxide. ~No equilibrium can be estab- 
lished in either case, for in the tissues oxygen is con- 
tinually being used and carbon dioxide is continually 
being formed. 



RESPIRATION 29 

Free Oxygen. — In breathing, animals use free oxygen 
as it exists in air; they do not take it from water or 
from any other compound containing oxygen. Animals 
that are habitually surrounded by water get their oxygen 
from air that has entered the water by the process of 
diffusion. The water brings the air in contact with 
the membrane, and oxygen enters and carbon dioxide 
passes off in the manner described above. 

Equilibrium of Nitrogen. — Oxygen and carbon di- 
oxide are the only gases in air that are concerned in 
respiration. Any gas that is in the air, however, may 
enter the body. Air is composed principally of oxygen 
and nitrogen. Nitrogen as well as oxygen passes 
through the membrane, but, as living organisms do not 
as a rule use free nitrogen, it establishes an equilibrium 
and does not concern itself with the activity of the body 
except under extraordinary conditions. 

Respiration in Specific Animals. — In considering the 
respiration of any specific animal it is necessary (1) to 
locate the moist membrane, (2) to ascertain the means 
by which air is brought in contact with the membrane. 

Lower Animals. — In one-celled animals the process is 
simple. It takes place at any point on the body's sur- 
face, for the animal is merely a mass of protoplasm 
surrounded by a membrane (Fig. 16). Oxygen is dis- 
solved in the water in which the animal lives; as it 
comes in contact with the surface of the animal it enters 
because its pressure is greater in the water than in the 
body of the animal. The pressure of oxygen is always, 
low 7 in the animal because as soon as it gets inside it is 
carried to all parts of the cell and is used in the manu- 



30 PHYSIOLOGY 

facture of new protoplasm. As carbon dioxide is 
formed in this process its pressure is always greater in 
the body of the animal than in the surrounding water. 
It therefore passes out of the animal. 

In the next higher group of animals the tissues are 
still simple enough to allow the gases in the water that 




Fig. 16.— Ameba. (From Hertwig, after Leidy.) cv, contractile vacuole ; n, 
nucleus ; iV, food-vacuoles. 

bathes them to pass through. Their manner of breath- 
ing therefore does not differ from that of one-celled 
forms. 

Higher Animals. — As animals become more highly 
developed the number of cells in the body increases, 
division of labor occurs and similar cells become grouped 
into tissues, each with its own special work. As the 
whole body is then no longer adapted to the absorption 



RESPIKATION 



31 



of oxygen, a special membrane is se1 pparl for this 
function. This menus (1) that the oxygen comes into 
the body a1 a definite point, (2) thai this oxygen must be 
transferred from this point to every cell in the body. 
The blood is the carrier. It comes to the tissues laden 
with oxygen. In the tissues the pressure of oxygen is 
low and the pressure of carbon dioxide is great. Oxygen 
therefore passes into the tissues and carbon dioxide 
passes into the blood. When the blood comes again in 




Fig. 17. — The passage of oxygen and carbon dioxide between the blood and the 
lymph in the tissues. 

communication with air it gives up this carbon dioxide 
and receives a fresh supply of oxygen (Fig. 17). 

Respiratory Organs in Aquatic Animals. — In aquatic 
forms such as lobsters, oysters, and fish the membrane 
that has been specialized for breathing is located on the 
surface of the gills (Fig. 18). The gills lie on each side 
of the body so near the surface that water can continually 
bathe, them. They consist usually of a feathery out- 
growth, or of two double flaps, covered with a very thin 
membrane. 



32 



PHYSIOLOGY 



Relation Between the Blood and the Gill Membrane. 

— Immediately under this membrane is a network of 
blood vessels with very thin walls, which connect the 
gill surface with every other part of the body. The air 




Fig. 18.-^1, Gills of a crayfish exposed by cutting away the shell. (From Hertwig.) 
B, Larval form showing external gills. (From Hertwig, after Sarasins.) 



in the water is separated from the blood by only the thin 
gill surface and the walls of the blood vessels. By 
osmosis, any gas in solution in the water can find its way 
into the blood and any gas in solution in the blood can 
find its way into the water. Relative pressure governs 
the process. As in one-celled animals, oxygen passes into 
the blood, for its pressure is greater in the water than 
in the blood ; and carbon dioxide passes into the water, 
for its pressure is greater in the blood than in the w.ater. 
Situation of the Moist Membrane. — If one of these 



KESPIRATION 33 

animals wore taken from the water and lefl exposed 
to the air, it would die for lack of oxygen, although there 
is such a large proportion of oxygen in the air, because 
oxygen can pass through a membrane only when the 
membrane is moist. In these animals, the membrane 
is situated practically on the outside of the body. It 
is kept moist by the water in w T hich they live, but it 
would soon become dry and hard if exposed to the air. 
In animals not surrounded by water the membrane is 
protected by being situated in a moist chamber so far 
removed from the surface that it can not dry out. In 
insects it lines branching tubes ; in other land animals 
it is developed into special organs called lungs. 

Respiratory Organs in Land Animals. — Each lung 
is like a bunch of hollow grapes, with very thin skins. 
Each grape-like hollow is filled with air and is called 
an air cell. The thin skin is an elastic membrane in 
which is a network of tiny blood vessels. The air inside 
the air cells is thus separated from the blood in the 
blood vessels by a thin, moist membrane which can not 
grow dry because the lungs are situated in a moist 
chamber. Oxygen from the air inside each air cell 
can pass into the blood through the lung membrane 
as easily as it passes from water into the blood of the 
fish through the gill surface. 

Mechanism for Bringing Air in Contact with the 
Membrane. — Lungs are so far removed from the surface 
of the body that a special mechanism is necessary to 
bring the air into the air cells in contact with the lung 
membrane. This mechanism is beautifully developed 
in human beings but it is not peculiar to them. It 



34 



PHYSIOLOGY 



might be studied to advantage in a cat or a dog, for the 
conditions are similar. 

How does the air get inside the air cell ? Each little 
air cell has a tiny tube opening into it which in turn 
opens into a larger tube and this into a still larger tube 
until we find that the whole mass of air cells in each lung 
opens into one large tube (Fig. 19). The tubes from 

the two lungs unite to form 
the trachea or windpipe 
(Fig. 20). Air that finds 
its way into the windpipe 
thus has free access to each 
little sac. As the behavior 
of the lungs, as a whole, is 
only the concerted behavior 
of all the cells, we may 
think of each lung as a hol- 
low bag, a single enlarged 
air cell (Fig. 25, L). 

What makes the air go 
into the lungs ? It is again 
a case of air pressure. If 
the pressure of the air is 
greater outside than inside 
the air rushes through the 
windpipe into the lungs ; if 
it is greater inside than 
This occurs at fairly regu- 
lar intervals and is due to a rhythmical change in the 
pressure of the air within the lungs. 

Respiratory Muscles. — What causes the alternate 




Fig. 19.— Air cells and bronchial tubes. 

outside the air rushes out. 



RESPIRATION 



35 



change in pressure? If depends upon the situation of 
the lungs in the body, [f we disregard the legs, arms, 
and head, the body is like a barrel. The hollow space 
inside contains various organs busy with the life proc- 




Fig. 20.— Front view of trachea and its branches. Ep., Epiglottis; Lar., Larynx ; 
Th., Thyroid Cartilage; O., Cricoid Cartilage; JR., Ring of Cartilage; B.l. % 
Left bronchus ; C, Chest wall and ribs. (From Fitz.) 



esses. In higher animals this cavity has a partition 
stretched across it. This partition regulates to a great 
extent the pressure in the lungs. It is not an immov- 
able partition, but one that is capable of a great deal of 
activity. It is made of a muscle called the diaphragm 
in which the fibers are arranged like the radii of a 



36 



PHYSIOLOGY 



circle (Fig. 21). As each fiber contracts, the entire cir- 
cle becomes smaller. When the fibers are relaxed the 




Fig. 21.— Front view of diaphragm and its attachments. "P.c, Vena cava ; S.> 
Sternum; C, Cartilages of ribs; Ao. y Aorta; D.t., Central tendon of dia- 
phragm ; Es., (Esophagus; D.p. y Pillars of diaphragm. (From Fitz.) 



diaphragm is too large to make a flat partition across 
the barrel-like body, and we should expect it to hang 
down, but apparently against the laws of gravity it 
hangs up (Fig. 22 ? A). When the fibers contract the 
diaphragm flattens out and the upper cavity becomes 
longer than it was before (Fig. 22/ B). 

At the same time the muscles in the outside wall of 
this cavity contract and lift the ribs. Because of the 
peculiar shape of the ribs, the cavity becomes larger both 



RESPIRATION' 



37 



from side to side and from back to front when they 
are lifted (Fig. 23 and 24). 




Fio. 23.— Diagram illustrating the position of the diaphragm, A, when relaxed ; B, 
when contracted. 



i! 1st 





F13. 23.— Diagram illustrating the 
dorso-ventral increase in the di- 
ameter of the thorax when the 
ribs are raised. (From Martin.) 
ab, vertebral column; c, c?, two 
ribs in expiration; c', d\ their 
position in inspiration ; st, ster- 
num in expiration; st', sternum 
in inspiration. 



Fig. 24.— Diagram illustrating the posi- 
tion of the chest in A, expiration and 
B, inspiration. (From Fitz.) 



These muscles are stimulated when there is an excess 
of carbon dioxide in the blood. They therefore con- 



38 



PHYSIOLOGY 





tract rhythmically and involuntarily. By their con- 
traction the upper cavity is automatically increased in 

size in every direction. 
Inspiration. — The 
lungs are situated in 
this cavity and their 
delicate elastic bags re- 
spond to every change 
in the size of the cav- 
ity (Fig. 25). As the 
cavity becomes larger 
they become larger and 
the pressure of the air 
inside the lungs be- 
comes less than the 
pressure outside. Im- 
mediately the air from 
the outside rushes 
through the windpipe 
into the lungs until an equilibrium is established. This 
process is called inspiration (Fig. 26, A). 

Expiration.— When the muscles contract the reverse 
happens. The chest cavity contracts, the lungs become 
smaller, the air in the lungs becomes denser than the air 
outside, and passes out. This process is called expira- 
tion (Fig. 26, B). 

Effect of the Elasticity of the Lungs on the Dia- 
phragm. — As the air goes out, the lungs, which were 
stretched by the incoming air, tend to resume the 
smallest area. They push away from the diaphragm 
with a force equal to their elasticity so that the pres- 



Fig. 25. — Diagram of apparatus to illustrate 
the effect of the position of the diaphragm 
on the lungs. B, bottle with bottom re- 
moved ; ilf, flexible elastic membrane 
pulled by string, S; L, an elastic bag 
representing the lungs. It communicates 
with the external air by a glass tube fitted 
air tight through a stopper. 



RESPIRATION 39 

sure above the diaphragm is slightly less than the atmos- 
pheric pressure and consequently than the pressure 





Fig. 26.— Diagram to show the position of the sternum, diaphragm and abdominal 
wall in A, inspiration and B, expiration. The shaded area represents the 
stationary air, the unshaded area in A, the increased air space in inspiration. 

below it. This causes the peculiar behavior of the dia- 
phragm in hanging upward. 

Phraseology. — The word respiration is used some- 
times to refer to inspiration and expiration, and some- 
times to the passage of gases through a membrane. To 
prevent confusion the passage of gases through a mem- 
brane has been called internal respiration, and the move- 
ment of the chest external respiration, but it seems 
clearer to restrict the word respiration to the essential 
process that occurs in all animals and reserve the words 



40 



PHYSIOLOGY 



inspiration and expiration for the special process that 
brings the gases in contact with the membrane occurring 
only in higher animals. 

Hygiene of Respiration. — There is not so much dif- 
ference as is ordinarily supposed between fresh air that 
is taken into the lungs and impure air that is given off ; 

Deep 
breathing 



Moderate 
breathing 



Quiet 
breathing 








' 


_ — 





_ 





— 




— : 










-Fresh air 



- Air left 

in lungs 



Fjg. 27.— Diagram showing the relative amounts of fresh and stale air in the lungs 
at different depths of breathing. (From Fitz.) 

the one contains about 20 per cent, of oxygen and but 
a trace of carbon dioxide, the other about 16 per cent, 
of oxygen and 4 per cent, of carbon dioxide. Four parts 
out of every hundred do not seem a large proportion of 
carbon dioxide, and yet this air is utterly unfit to be 
breathed in again, for the body is unable to get from it 
sufficient oxygen for its nourishment. In addition, this 
air is directly poisonous, for it contains poisonous sub- 
stances from the body and in many cases disease germs. 



RESPIRATION 



41 



The air cannot be entirely forced from the lungs. 
Even after the most forced expiration some air will still 
remain in them (Fig. 27). If this air is not frequently 
and thoroughly changed it will make an excellent 
medium for the growth of disease germs. Most disease 
bacteria do not thrive well in the presence of oxygen, but 
thrive admirably in its absence. People therefore who 
practice collar bone breathing exclusively are apt to 
leave the lower part of the lungs unused (Fig. 28). 

ABC 






Fig. 28.— Types of breathing. A, corsetted figure, clavicular or collar bone breath- 
ing ; B, male figure, abdominal breathing. Pressure of clothing and faulty 
position impedes expansion of the chest. C, figure properly posed and free 
from constriction. (After Coleman.) 

They succumb much more easily to tuberculosis than 
those who breathe deeply. 

Diaphragmatic breathing may be cultivated by sim- 
ple exercise. Place the hands beside the lower ribs on 
each side of the body and force the ribs out against the 
hands. This will enlarge the chest cavity and air will 
enter. It is not necessary to suck in the air. The lungs 
are passive. They need not be considered, for they have 



42 PHYSIOLOGY 

no power of initiation whatever. In order to improve 
the mechanism of inspiration all that is necessary is to 
strengthen the muscles which control the enlargement of 
the chest cavity. If at the same time the throat and jaw 
are relaxed the air will pass in and out easily and the 
voice will improve in quality. Few people use the voice 
as it should be used. Either they breathe improperly 
or they contract the muscles of the throaty tongue and 
jaw; or perhaps both. For purely aesthetic reasons it 
is worth while to cultivate a good speaking voice, for 
hygienic reasons it is even more important. A large 
amount of the wear and tear of our modern life comes 
from the unpleasant noises to which we are subjected. 
An unpleasant voice which must be heard from morning 
till night will rasp the nerves of the strongest person. 
Even though he may be unconscious of it, it will 
also react on the nerves of its possessor, for a rasping 
voice usually means a rasped throat and an undue call 
upon nervous energy. The beautiful voice of Sara 
Bernhardt, which even in a whisper reaches without 
effort the utmost limit of the largest theatres, is due 
not so much to a natural gift as to her patient cultivation 
of a wonderful diaphragm and of the power of relaxa- 
tion. For the sake of improving the voice, of avoiding 
disease and of strengthening the whole body, it is worth 
while to cultivate the muscles which control inspiration 
and provide the preliminary condition for effective respi- 
ration. 

Summary. — When an animal breathes, oxygen passes 
into its body and carbon dioxide passes out. All living 
animals have the whole or a part of the body covered 



INSPIRATION 43 

with a moist membrane. When a gas comes in contact 
with this membrane the freely moving particles of the 
gas pass through the spaces between the particles of the 
membrane. 

In one-celled animals (1) The membrane covers the 
entire body surface. (2) Oxygen is dissolved in the 
water which continually bathes the surface. (3) This 
oxygen is carried to all parts of the body by the con- 
stant circulation of the protoplasm and enters into vari- 
ous chemical actions that finally result in the formation 
of carbon dioxide. (4) The carbon dioxide passes off 
into the water. This simple process has become com- 
plicated in higher organisms by certain peculiarities of 
development. 

In many-celled animals the membrane is located in a 
definite place and the oxygen passes first into the blood. 
The blood carries it to all parts of the body and brings 
back carbon dioxide that it receives along its way. 

The passage of oxygen into the blood and the passage 
of carbon dioxide into the water are independent of each 
other. In neither case can an equilibrium be established 
because the incoming oxygen is continually passing from 
the blood into the cells where it is used, and the outgoing 
carbon dioxide is continually passing from the cells 
where it is formed into the blood, so that in the blood the 
pressure of oxygen is kept continually less and the pres- 
sure of carbon-dioxide is kept continually greater than 
in the water outside. 

In higher animals the membrane is far removed from 
the surface of the body for protection. A complicated 
mechanism is therefore necessary to bring air in contact 



44 PHYSIOLOGY 

with the membrane. By a contraction of the diaphragm 
and of the muscles that lift the ribs, the chest cavity 
is enlarged. Inspiration occurs and fresh air is brought 
in contact with the lung membrane. When the muscles 
relax the cavity becomes smaller, expiration occurs, and 
the impure air is removed from contact with the mem- 
brane. 

These processes do not happen by accident. Neither 
do they happen because we need them to happen. Every 
phase of the process of respiration is governed by a defi- 
nite law. A gas always passes in the direction of the 
least pressure. In accordance with this law we will get 
the oxygen that we need if we do our part by seeing to it 
that the air about us is reasonably pure and that our 
muscles are strong enough to keep a good supply in con- 
tact with the lung membrane. But if we do not do our 
part, if, for example, we sit in an ill-ventilated room, 
we will not get the oxygen that we need. The law will 
act whenever gases are in contact with the membrane, 
but from vitiated air not oxygen but poisons enter the 
body. 

The health of the entire body is dependent upon respi- 
ration. Give the healthy body plenty of oxygen and if it 
is not abused in any way it will probably remain healthy. 
Deprive the body of oxygen and it cannot remain 
healthy. 



CHAPTER III 
ASSIMILATION 

Steps in the Process. — Living matter has the power to 
take in substances called foods and out of them to manu- 
facture new living matter. The process by which foods* 
are converted into the body substance is called assimila- 
tion. 

Broadly the word includes all the steps in the process. 
We must therefore consider (1) The nature of food. (2) 
The way it is taken into the body. (3) The way it is 
made fit for the use of the body. (4) Its transportation 
to all parts of the body. (5) Its conversion into proto- 
plasm and other unstable substances. (6) The elimina- 
tion of waste materials. In this broad sense respiration, 
which provides much of the oxygen that is used in the 
manufacture of protoplasm and in the oxidation of 
wastes, and circulation, which carries substances from 
place to place in the body, are phases of assimilation. 
In this chapter we shall confine our attention to the 
assimilation of the food that we eat. 

Nature of the Process. — It is clear that young animals 
must assimilate food, for they could not grow were it not 
for the addition of new material. But why should an 
animal continue to form new protoplasm after it has 
reached its full size ? 

45 



46 PHYSIOLOGY 

The body is like a steam engine. Heat furnishes it 
with the power to move. This heat comes from chemical 
action. Whenever an animal moves, protoplasm, or some 
other unstable compound, splits into simpler substances 
and sets free heat. This heat causes other compounds 
to disintegrate, or simple substances to combine, until, 
through a series of chemical changes all of which set 
free heat, the food is converted into new complex com- 
pounds which replace the old ones that have split up, 
and wastes are formed which are given off from the 
body through an excretory organ. 

Were it not for the assimilation of food the body 
would waste away as a result of activity. The more 
active the body then the more food is necessary. A 
laborer must eat more to keep the body in good condition 
than a bank clerk ; and a growing child must eat more in 
proportion than a man, for the child's food must not 
only replace what is lost through activity but it must 
provide for growth. 

In One-Celled Animals. — Assimilation is a universal 
process. It occurs in all organisms. With the com- 
pound microscope we may see one-celled animals take in 
food and give off wastes. The food surrounded by a 
drop of water passes directly into the protoplasm and 
the part that is unfit for use is eliminated through a 
weak spot in the body wall. This material never be- 
comes part of the body, and it must not be confused with 
waste from the protoplasm. The nutritive part of the 
food is carried about in the circulating stream until it is 
converted into protoplasm. Waste from disintegrated 
protoplasm leaves the body through a pulsating vacuole, 



ASSIMILATION 



47 



a clear spol thai alternately appears as if becomes filled 
with fluid and disappears as the fluid is emptied into the 
water outside. 

In Many-Celled Animals. — The simple process in 
one-celled animals has all the essential features that char- 
acterize higher forms. In many-celled animals an organ 
is set apart for the reception of food. As the cells in 
the young animal begin to develop they become arranged 
in the form of a hollow sphere. At one point on the sur- 
face of the sphere the cells push in until they reach the 
opposite surface. This structure, called the gastrula, 
is bag-like. The wall is made of two layers of cells and 
the cavity opens to the outside by a single opening. The 
cells on the inside soon grow different from those on the 





Fig. 29.— Formation of gastrula. (From Hertwig, after Hatschek.) 



outside and become adapted to the assimilation of food. 
This is the primitive digestive tract (Fig. 29). 

A great number of animals are still in the gastrula 
stage. Though they differ widely from each other, they 
are classed together, for they have one characteristic in 
common. The single cavity in the body is adapted to 
the assimilation of food and it has but one opening to 
the outside. Through this opening food enters and unfit 



48 



PHYSIOLOGY 



material passes out. The food is made fit for use in the 
cavity, passes into the cells lining the cavity and thence 
to all parts of the body. In most of these animals the 
cavity is bag-like (Fig. 30 A), but in jellyfish it is a 
well-defined tube (Fig. 30 B). This tube-like charac- 




Fig. 30 A.— Digestive tract of the 
hydroid. (See Fig. 36, A.) 



Fig. 30 B.— Digestive tract of the 
jellyfish. (See Fig. 36, A.) 



ter is a marked characteristic of the alimentary system 
in all higher animals and gives rise to the name ali- 
mentary canal that is often used to designate this organ 
of the body. 

The Complete Digestive Tract. — In the next group 
of animals a further development occurs which also be- 
comes an important characteristic of all higher animals. 
The tube develops a second opening to the outside. 
Food then enters through one opening and refuse passes 
off through the other. Special organs exist for the 
eliminating of waste substances which result from the 
splitting up of protoplasm. In almost all animals, then, 
the digestive system is a tube open at both ends to the 



ASSIMILATION 



49 



outside. The shape of the tube, its length, and the way 
it lies in the body differ in the various groups, but it 
bears a close relation to the shape of the animal and to 
the character of its food. 

Variations in Development. — The starfish is a flat, 
five-raved animal. The tube passes through the animal 
from the dorsal, or upper, to the ventral, or under, 
side, and is very short. It swells out into two 




Fig. 31.— Digestive tract of the starfish (section). (See Fig. 36, B.) 

enlargements or stomachs, each of which has five 
pouches corresponding to the five rays (Fig. 31). 




Fig. 32.— Digestive tract of the earthworm. (See Fig. 36, B.) 



The lobster and the earthworm are elongated. The 
tube is correspondingly long and straight, and the stom- 
achs comparatively small (Fig. 32, Fig. 33). In 




Fig. 33.— Digestive \ract of the lobster. (See Fig. 36, B.) 



clams as the tube is too long to pass directly through 
the body, it becomes twisted on itself (Fig. 34). In 



50 



PHYSIOLOGY 



higher animals the tube is more highly developed. 
The enlarged stomach is sharply defined; the tube is 




Fig. 34.— Digestive tract of the clam. (See Fig. 36, C.) 

very long in proportion to the length of the body, and 
is consequently very much twisted on itself (Fig. 35, 




Fig. 35.— Digestive tract of a vertebrate. (See Fig. 36, C.) 

Fig. 36) ; and special glands are developed from it 
which manufacture special digestive fluids. 

Diet of Animals. — The diet of animals varies greatly. 
Some animals live entirely upon plants, others eat only 
the flesh of other animals, still others eat a mixture of 
plant and animal tissues. Gradually animals have be- 
come adapted to the diet which in the beginning was 
adopted either through choice or through necessity and 



ASSIMILATION 



51 



which proved besl suited to their Deeds, and they could 
not now exchange diets. Grain-eating animals have 
teeth fitted for grinding and a well-developed system 





Fig. 3C— Diagram to illustrate the development of the alimentary canal in the 
advance from lower to higher forms. 

for digesting plant tissues. Flesh-eating animals have 
teeth fitted for tearing flesh and crushing bone, and a 
less highly developed system for the digestion of flesh. 
Animals that eat a mixed diet have both kinds of teeth 
and a digestive system which in size and structure lies 
between the two extremes. 

The Five Food Substances. — Although diets vary, we 
find that the foods that animals eat differ only super- 
ficially. Xo matter what an animal eats there are con- 
tained in it only the five food substances : water, salts, 
carbohydrates, hydrocarbons, and proteids. These all 
animals must have. 

Water. — Water is contained to a greater or less ex- 
tent in everything that we eat. It is possibly the most 
important of the food substances, for not only does it 
act as a food but also as a solvent of other food sub- 
stances. These can not enter the cells unless they are 
dissolved, for only liquids or gases can pass through the 



52 PHYSIOLOGY 

cell-walls. As water is a liquid it passes through easily 
and carries with it everything it holds in solution. In 
its natural state water always contains substances in. 
solution which are good for the body. We should there- 
fore drink large quantities of it, but we should be careful 
that it is pure and uncontaminated by disease germs. 

Salts. — Salts are contained in the water that w T e drink 
and in almost everything that we eat. Table salt, or 
sodium chloride, is the most important of these, for it is 
constantly lost from the body through perspiration and 
other excretions, and it is necessary to the composition 
of the blood and the maintenance of the right propor- 
tion of water in the tissues. Animals that live on grains 
poor in salt often travel many miles in order to reach 
salt licks. As salts are so readily dissolved in water, 
they undergo no change before entering the cells of the 
body. 

Carbohydrates. — Carbohydrates include cellulose, 
starch and sugar. They are manufactured by plants 
from water and carbon dioxide. They are therefore 
found in varying amounts in most plant tissues. As 
animals eat the plant tissues they are also found in the 
bodies of animals. They consist of carbon, hydrogen 
and oxygen in such proportions that there is always 
twice as much hydrogen as oxygen. They are called 
carbohydrates, a name that means carbon watered, 
because two parts of hydrogen and one of oxygen form 
water. 

Hydrocarbons. — Hydrocarbons include all fats 
and oils. They are found in the tissues of both plants 
and animals. They contain carbon, hydrogen and oxy- 



ASSIMILATION 53 

gen, but there is more than enough hydrogen to form 
water. The excess of hydrogen Is responsible for the 
name hydrocarbon. 

Proteids. — Proteids are practically identical with 
dead protoplasm. We eat them whenever we eat the 
tissues of plants or animals. In animals there is a 
larger proportion of proteids and fats and a smaller pro- 
portion of starches than in plants. Chemical analysis 
shows that proteids are conrposed principally of carbon, 
hydrogen, oxygen and nitrogen. In addition they may 
contain traces of sulphur and phosphorus. They are 
especially important because of the nitrogen that they 
contain. Xitrogen is absolutely necessary to the manu- 
facture of protoplasm, and as animals can not use free 
nitrogen from the air they can obtain it only from the 
proteids that they eat. 

Necessary Proportions of Food Substances. — With- 
out proteids the body would starve very quickly, but it 
could subsist for a considerable period without starch or 
fats. These substances are especially useful because 
they are completely oxidized in the body and conse- 
quently set free an enormous amount of heat. In gen- 
eral, the amount and character of the food required by 
man depends on the amount of work that he does. W 7 e 
find that although the diet differs in different countries, 
men who do the same amount of hard work eat approxi- 
mately the same quantity of food made up approximately 
of the same proportions of carbohydrates, hydrocarbons 
and proteids. 

Nutriment in Food Stuffs. — Cereals furnish more 
nutriment in proportion to weight and cost than other 



54 PHYSIOLOGY 

foods. Wheat, oats or corn with some form of fat 
forms an almost perfect food, that is, a food which 
contains the proper proportions of proteids, fats and 
starches. Bread and butter lack only a small amount 
of proteid. Most breakfast foods are very bulky in 
proportion to the amount of nutriment they contain. 

Vegetables are especially valuable because they con- 
tain large quantities of sugar and starch. Some of 
them are rich in proteid. They are valuable also be- 
cause they contain salts and cellulose. Cellulose is not 
nutritious but it is useful mechanically, for through its 
bulk it aids the movement of the food through the canal. 

White potatoes, sweet potatoes, tapioca, bananas, are 
rich in starch; melons, grapes, beets, in sugar; peas, 
beans, peanuts, nuts, in proteids; olives, nuts, in fats; 
cabbages, turnips, in cellulose. 

Milk and Eggs are very nearly perfect foods. Milk 
contains water, salts, proteids, fats and sugar. Eggs 
lack carbohydrates. 

Meat is valuable because it contains a great deal of 
proteid that is more easily digested than plant proteid. 

Condiments such as spices, mustard, ginger, pepper, 
stimulate the appetite but contain no nutriment. 

Beverages. — Tea and coffee are stimulating but not 
nourishing. Cocoa and chocolate have a slight food 
value on account of the fat they contain. These sub- 
stances are not necessarily harmful if taken in mod- 
eration with food, but they all contain a powerful drug 
which is distinctly harmful if taken habitually in too 
great quantities. Alcohol may be oxidized in the body, 
and for this reason there has been some discussion as to 



ASSIMILATION 



55 




its food value. It is so very harmful in its effects upon 
the nervous system, however, that it can not properly 

be considered a food. Water is the most wholesome 
beverage. 

Digestion. — When food is swallowed it is not really 
inside the body although it is in the 
alimentary canal. It is like a piece 
of dough that has accidentally 
dropped into the upright tube of an 
old-fashioned cake pan (Fig. 37). 
In order to get into the body it must 
pass through the cells that form the 
Avail of the canal. As starches, fats 
and proteids are insoluble, they must 
be made soluble before they can pass 
through the wall, that is, they must 
be digested. This is accomplished 
through the activity of certain com- 
plex and very unstable compounds 
called enzymes, or ferments, w 7 hich are produced by 
living cells. 

Enzymes. — There are a great many enzymes all of 
which have certain characteristics in common. They 
have no power to initiate a change, but they are able to 
hasten, or retard, a chemical, or physical action, so that 
it is able to take place under conditions which would 
ordinarily render it impossible. They act at very low 
temperatures and in exceedingly small quantities with- 
out being used up. 

Enzymes in the Digestive Juices. — The three classes 
of substances to be digested have three corresponding 



Fig. 37.— Diagram to il- 
lustrate the relation of 
a particle of food in 
the alimentary canal 
to the body. It does 
not enter the body 
until it has passed 
through the wall of 
the canal in the direc- 
tion of the horizontal 
arrows. 



56 PHYSIOLOGY 

classes of enzymes to act upon them. One changes the 
starches, another the proteids, and the third the fats, 
into soluble substances which can readily be absorbed. 
These enzymes are found in the various digestive juices 
of the body. The saliva, a digestive fluid found in 
the mouth, contains an enzyme which changes starch 
into a soluble sugar called maltose. In order that it 
may have time to do its work starchy foods should be 
thoroughly chewed. The other food substances are not 
changed by saliva, but they are moistened and are 
consequently swallowed more easily. 

The gastric juice which is secreted by small glands in 
the wall of the stomach also contains only one enzyme, 
pepsin. Pepsin changes proteids into soluble peptones 
but has no effect on starches and fats. The pancreatic 
juice contains three enzymes. The most important of 
these is called lipase. It changes fat into soluble fatty 
acid and glycerine. The other two enzymes act upon 
starch and proteid that escape digestion in the mouth 
and stomach. 

Reversible Action of Enzymes. — Very curiously the 
action of enzymes is reversible; that is, if an enzyme 
changes starch into sugar, it also changes sugar into 
starch. These actions take place simultaneously, and 
result in an equilibrium, or a condition of balance. 
Whenever there is an increase or a decrease of either 
substance the equilibrium is disturbed, and the action 
becomes more vigorous in one direction than in the other. 

If, for example, there is a surplus of starch, the 
starch is transformed into sugar more rapidly than 
the sugar into starch. 



ASSIMILATION 57 

Enzymes in the Tissues. — These enzymes are not con- 
fined to the digestive juices, [f they were, the change 

of food substances into protoplasm might be more com- 
plicated than it is. They may exist in any part of the 
body. Through their reversible action soluble substances 
may be changed into proteids, fats or starch, and stored 
in any part of the body ; or proteids, starch or fats may 
be changed into soluble form and carried by the blood to 
other parts of the body where they may be used by the 
protoplasm. Large quantities of proteids are stored in 
the muscles and in the blood ; starch in the muscles 
and in the liver ; and fat in any part of the body, though 
it is found in quantities most often just under the skin. 
In cases of starvation, these stored substances may be 
drawn upon, the fat first, and later the starches and 
proteids. 

Passage of Food Through the Canal. — Through a 
series of muscular contractions, food taken into the 
mouth is forced to pass down the canal. The tongue and 
cheek muscles help to hold the food between the teeth 
while it is chewed ; they then squeeze it into the cavity 
at the back of the mouth, over the top of the windpipe 
which is closed by a swinging lid, into the oesophagus, 
which relaxes to receive it. The oesophagus then con- 
tracts behind the food and relaxes before it, until it 
reaches the stomach, a small pear-shaped bag, which 
holds about three pints when it is moderately distended. 

During the first hour and a half the opening into the 
small intestine is very small and only the dissolved 
starches and proteids pass through. Later the opening 
becomes larger and other substances pass through easily. 



58 PHYSIOLOGY 

As they pass through, the pancreatic juice and the 
secretion of the liver, the bile, which seems to aid the 
digestion of fats, are poured in upon them. After about 
two and a half hours the stomach is empty, and ready 
for a period of rest. Digestion continues in the small 
intestine and absorption occurs. The soluble substances 
pass through the cell walls into the blood, which carries 
them to all parts of the body. The residue of the food 
passes on into the large intestine through a series of 
contractions similar to those that take place in the 
oesophagus. 

Absorption in the Intestine. — A special mechanism 
fits the small intestine for absorption. Finger-like pro- 
cesses called villi project from the inner wall (Fig. 38). 
These contain a network of connective tissue, muscle 
fibers, blood vessels and spaces connected with tube-like 
channels called lacteals. Peptones and sugar pass into 
the blood and are carried to the liver. Fats enter the 
lacteals and reach the blood without being carried to the 
liver. In the blood, peptones are changed back to pro- 
teids and the fat emulsion is changed back to fat. The 
sugar remains sugar until it gets to the liver, when it is 
changed to starch. 

The residue that passes into the large intestine is not 
fit to nourish the body, but as long as it remains in the 
intestine chemical action continues, and poisonous sub- 
stances are formed which may be absorbed by the body 
through the process of osmosis as readily as substances 
which are nutritious. Therefore it is of importance 
not to allow this residue to remain in the alimentary 
canal until the system has been poisoned by it. 



ASSIMILATION 



59 



Excretory Organs. — This residue is no1 to be regarded 
as a true excretion, except in so far as it may contain 

cast-off cells from the wall of the canal. The faecal 




■L.Gl 



^ K«c 






Fig. 38.— Small section of the wall of the intestine showing three villi. In A, art- 
tery, vein and lacteal with their branches are represented ; in B, artery, vein 
and branches; in C, the lacteal only; Cap., Network of capillaries; 31. ep., Ep- 
ithelial membrane; Lac, Lacteals; In. 1., Level of inner wall of intestine ; GL, 
Gland; A., Artery; 7., Vein; In.2., Outer wall of intestine; VI., Villi ; L. GL, 
Layer of glands (mucous layer); L.c, Layer of cells and muscle. (Diagram- 
matic.) (From Fitz.) 



matter has never been truly a part of the body, for it is 
made of those parts of the food which were undigested 
or unfit for digestion. True excretion is effected through 
the kidneys, the lungs and the sweat glands. 

The wastes of the body are principally carbon dioxide, 



60 



PHYSIOLOGY 



water and urea. Carbon dioxide and water vapor, by 
osmosis through the lung tissue, pass from the blood 
to the air in the lungs and are removed from the body. 
Solids are not able to do this. Special organs therefore 



\ V 




Fig. 39.— Excretory organ of the earthworm. W, body wall ; 0, opening to the out- 
side ; S, septum. The tube passes through the septum and opens through a 
funnel-shaped ciliated mouth into the body cavity. 

prepare them for removal and they leave the body 
in solution in water (Fig. 39). 

The Kidneys. — The kidneys, two reddish brown, 
bean-shaped bodies, lie on each side of the spinal column 
under the lowest ribs (Fig. 40). Large arteries enter 
them and become subdivided into small capillaries which 
penetrate every part of the tissue. Later these reunite 
into veins which carry the blood from which the waste 
has been removed back to the heart. The capillaries 
gather together in small masses, each of which becomes 
surrounded by a cup which opens into a tube closely 
wrapped about by capillaries (Fig. 41) d Through the 
thin walls of these capillaries water carrying wastes, 
principally urea in solution, passes into the cups or 
directly into the tubes. The tubes unite and empty 
eventually into the bladder through a large tube called 



ASSIMILATION 



61 




Fig. 40.— The renal organs viewed from behind. (From Martin.) J?, right kid- 
ney ; A, aorta ; Ar, right renal artery , Vc, inferior vena cava ; F>\ right re- 
nal vein; U, right ureter j Fw, bladder ; Ua, commencement of urethra. 



62 PHYSIOLOGY 

the ureter. The amount of water that is removed from 
the blood in this way depends on the amount that has 
been drunk. Normally it is about three pints daily. 

Urea. — Urea (N 2 H 4 CO) is formed by the splitting 
up of proteids. It therefore contains a large amount of 
nitrogen. As it is an incompletely oxidized substance, 
the body does not get so much heat in proportion from 
the splitting up of proteids as it does from the splitting 
of fats and starches, which give rise to water and carbon 
dioxide, completely oxidized substances. 

The Sweat Glands. — The sweat glands are very tiny 
(Fig. 42). They are scattered over the body in the 
layer of fat immediately under the skin. The " pores " 
are the openings of minute ducts that lead from them 
to the surface of the skin. Their secretion is composed 
normally of water, salt and the products of the sebace- 
ous glands; but if the kidneys fail to do their work 
properly the substances ordinarily secreted by them ap- 
pear in the perspiration. The amount of the secretion 
may be a quart or more daily, depending on the activity 
of the kidneys, on the temperature and on the amount 
of exercise. 

Hygiene of Digestion. — The hygiene of digestion is 
possibly more important than that of any other function. 
Many eminent physiologists and physicians attribute 
the majority of bodily ills to abuse of the digestive sys- 
tem. Not only must we have palatable food in sufficient 
quantities, but it must combine the right proportion of 
proteids, fats and starches. The thought alone of some- 
thing that we particularly like causes the mouth to 
water. Exactly the same thing takes place in the 



ASSIMILATION 



C3 



stomach when attractive food is eaten. The digestive 

juices are produced in larger quantities and in better 
quality, and the food has a better chance of being prop- 
erly digested. This fact is often disregarded. Some 
people 1 advocate uncooked food, but not only does cook- 




Fig. 41.— Structure of kidney, showing the secreting mechanism. The arrows in- 
dicate the direction of the flow of the fluids. U.I., beginning of urinary 
tubule ; Cap., Tuft of Capillaries; A., Artery; 711., Vein to tubule; V.2., Vein 
from tubule; U.2., Urinary tubule; Cap.M., Capillary mesh over tubule; 7. f 
Vein. (From Fitz.) 



ing render meats and most vegetables more palatable, 
but it is a safeguard against disease germs. It is better 
to keep the body well than to cure it of disease. Health- 
ful living, which includes proper care of the diet, will 
do much toward keeping the body in good condition, and 
often a change in diet will enable one to dispense with 
drugs that might otherwise be taken. 



64 



PHYSIOLOGY 



It is important that food should be properly chewed. 
In order that the enzymes may digest food they must 
come directly in contact with food particles. If large 
pieces are swallowed, the enzymes come in contact with 




Shut. 



Fig. 42.— Section of skin highly magnified showing sweat glands. Ep., Epidermis; 
Z>., Dermis; Sub. T., Subcutaneous tissue ; a, Shaft of hair ; b, Horny layer of 
skin ; c, Duct of sweat gland ; d, Papilla ; e, Capillaries of papillae ; /, Sebaceous 
glands; g, Connective tissue; 7i, Erector muscle of hair ; i, Artery; k, Hair fol- 
licle; l y Coil of sweat gland ; m, Artery to sweat gland; w, Papilla of hair; o, 
Connective tissue; p y Fat. (From Fitz.) 



the surface only. Only the outer surface will then be 
digested. Undigested masses are thrown into the intes- 
tine, fermentation takes place and poisonous substances 
are absorbed. Food should be chewed until it no longer 
has a specific taste and until it is a homogeneous mass. 
Chewing keeps the teeth in good condition by pro- 
viding them with exercise. Most dentists say that a 



ASSIMILATION '65 

large part of their trade depends upon the fact that 
people chew their food insufficiently, or eal food that is 
too soft. Sudden changes of temperature from hot cof- 
fee to iced water, for example, may crack the enamel. 
The teeth should be eared for, otherwise they decay. 
They then not only cause great pain but they are not 
able to do their work well, which may result in serious 
indigestion or dyspepsia, and they become lodging- 
places for disease germs. 

Emphasis should be laid upon the fact that the body 
needs a large quantity of water to dissolve food and 
carry it throughout the body. Water should not, how- 
ever, be taken in large quantities with meals, because it 
dilutes the digestive juice and renders it less effective. 
Xeither should very cold water be taken at that time, as 
the digestive juices work only at certain temperatures. 
If water is taken immediately upon rising in the morn- 
ing and an hour or two before meals the desire for it 
with the meals will disappear for the thirst is already 
appeased. 

Bad cases of nervous indigestion and catarrh of the 
stomach have been cured by the simple expedient of 
drinking, an hour before breakfast, a quart of hot water 
containing a half teaspoonful of salt and the juice of 
half a lemon. The large quantity of water washes clean 
the walls of the alimentary canal so that they are more 
fit for the absorption of the digested food. 

Summary. — Every movement of the body is accom- 
panied by the disintegration of protoplasm, or other 
complex and unstable substances. These substances are 
replaced by new substances made through the assimila- 



66 PHYSIOLOGY 

tion of food. The series of chemical changes that occur 
in the process set free heat, which furnishes the motive 
power for the activity of the body. The foods fall into 
five classes : water, salts, proteids, fats and starches. 
The last three must be digested, or made soluble, before, 
they can be assimilated. This is accomplished through 
the activity of enzymes manufactured by the protoplasm. 
In the lowest animals the entire process of assimilation 
occurs in a single cell ; in higher animals a special organ 
is set apart for digestion which has the form of a tube 
of varying width open to the outside at both ends. A 
series of muscular contractions forces the food to pass 
through the tube. On the way, the food is acted on by 
enzymes, and the nutritious substances pass into the 
blood and are carried by it to every part of the body. 
Undigested material and material that can not be di- 
gested pass off from the other end of the tube. Wastes 
from the disintegration of protoplasm are given off 
through special excretory organs. 



CHAPTER IV 
CIRCULATION 

Necessity for Circulation. — Assimilation and respira- 
tion are rendered effective through circulation. As new 
protoplasm may be made in any part of the body, oxygen 
and food products, the materials involved in its manu- 
facture, must be transported throughout the body, and 
the wastes that result from its disintegration must be 
transported to a place from which they may be ejected. 

The System. — In one-celled animals the circulation 
of the protoplasm within the cell suffices for the distri- 
bution of substances through the body. 

In many-celled animals a special circulatory system is 
necessary, for substances taken in at a definite point 
must be transported to tissues which may be remotely 
situated. An elaborate network of tubes penetrate all 
the tissues. These tubes are filled with blood which is 
in constant motion, and through the blood the transfer 
of substances from place to place is effected. 

In Lower Animals. — In the lower animals the tubes 
are few in number and their comparatively simple ar- 
rangement is determined by the shape and size of the 
animal and the arrangement of the various organs in its 
body. In starfish, for example, a blood vessel encircles 
the mouth and sends off a branch into each one of the 

67 



68 



PHYSIOLOGY 



rays (Fig. 43) , while in the earthworm two long tubes 
connected by a series of encircling rings run lengthwise 
in the body (Fig. 44). 

In Higher Animals. — In higher animals the number 




Fig. 43.— Diagram of the circulatory system of the starfish. 

of tubes is greater and their arrangement is consequently 
more complex. There is a general similarity in all ani- 
mals that have four limbs attached to a trunk. Minor 
details such as the branching of the vessels may vary, but 




Fig. 44.— Diagram of the circulatory system of the earthworm. 

even from a frog one can get a fairly good idea of their 
arrangement in man. 

The most noticeable feature of the system is an en- 
largement called the heart. In very low animals it is 
a simple tube. In higher animals it begins as a tube but 



CIRCULATION 



GO 



its tube-like character is soou obscured, for it grows 
faster than the space iii which it is situated and becomes 
twisted upon itself in such a way that four chambers are 

formed. 

From the heart branch large tubes which become 
smaller and smaller through repeated division. The 
small tubes later reunite, forming larger and larger 
tubes which lead back to the heart. The blood is thus 
able to travel from the heart through the tubes to all 
parts of the body and back to the heart, making a com- 
plete circulation. 

Mechanical Factors which Control the Circulation. 
(1) The heart. The passage of the blood through the 
body is controlled by purely 
mechanical features. The 
heart furnishes the motive 
power. It pushes the blood 
forward through the tubes by 
means of its rhythmical con- 
traction. It is a hollow body 
divided by a partition into 
two unconnecting chambers 
each of which is subdivided 
into two connecting cham- 
bers called respectively the 
right and left auricle, and 
the right and left ven- 
tricle. Its walls are made 
entirely of short, powerful 
muscle cells so interlaced that they are strong enough to 
send the blood throughout the body and firm enough to 




Fig. 45.— Muscle cells of heart. B, 
Connecting branch ; C, Cement 
substance; iV, Nucleus. (From 
Fitz.) 



70 



PHYSIOLOGY 



prevent its escape through them (Fig. 45). When the 
chambers are distended with blood the walls contract 
until they force the blood out, they then relax and allow 
another supply to come in (Fig. 46). This contraction 




F IG . 46.— Diagram of heart during relaxation and contraction. A, auricle contract- 
ing to fill ventricle ; B, auricle filling, ventricle emptying into aorta. Ao., 
Aorta; Au.cav., Cavity of auricle; Au.v. F., Auriculo-ventricular valve; Ch.t., 
Chordae tendinae ; V. cav., Cavity of ventricle; Pap.m. y Papillary muscle. 
(From Fitz.) 



and relaxation cause the heart beat which can be felt on 
the left side of the chest. The thickness of the walls 
depends on the amount of work demanded of them. 
The auricles contract simultaneously and the blood 
passes into the ventricles. As this requires little force, 
the walls of the auricles are comparatively thin. The 
ventricles contract simultaneously and the blood is sent 
through the body. They exert greater pressure and their 
walls are correspondingly thick. 

(2) The valves. The blood is kept flowing continu- 



CIRCULATION 



71 



A 



ously in one direction by valves. These are situated: 
(a) between the auricles and the ventricles, (b) between 
the ventricles and the arteries and (c) throughout the 
veins. The valve between the auricles and the ventricles 
is like a swinging door that opens in one direction only. 
It opens in response to the pressure of the blood, allows 
the blood to pass through, and then swings shut. The 
blood can not then pass 
back into the auricle. At 
the outlet of the ventricle 
there are three flat pockets 
which allow r the blood to 
pass out of the ventricle, 
but when it attempts to 
return, they become filled 
with blood and swell out 
so that the opening is 
closed (Fig. 47). Simi- 
larly in the veins the 
valves open to allow the 
blood to pass toward the 
heart but close against its return. Without the valves, 
the flow in the veins would be backward, because of the 
diminution of pressure. 

(3) The closed system. The system is closed; that is, 
the irregularly branching tubes are so arranged that 
when the blood has been carried from the heart to all 
parts of the body it is gathered together and returned to 
the heart. The vessels through w 7 hich the blood leaves 
the heart are tough, thick-walled, highly elastic tubes 
called arteries. They divide and sub-divide into smaller 




Fig. 47.— Diagram of valves of veins. 
A, valve opened by blood passing for- 
ward toward heart ; B, valve closed 
by attempted return of blood; C, vein 
opened to show arrangement of 
valves. (From Fitz.) 



72 PHYSIOLOGY 

and thinner-walled tubes which penetrate into every part 
of the body. The finest of these are the capillaries. In 
these the wall is made of a single layer of flat cells placed 
edge to edge. It is so thin that the blood is brought in 
close contact with the tissues and by osmosis gives up 
readily the nourishing substances it contains, and takes 
away the waste products. The capillaries unite to form 
larger tubes called veins, that bring the blood back to the 
heart. The walls of the veins are very thin, for little 
work is required of them. The pressure is reduced in 
the capillaries, and in the veins not enough is exerted to 
urge the blood onward. It is sucked back into the heart 
by the alternate change of pressure in the chest cavity 
due to the movements of expiration and inspiration. 

The blood leaves the left ventricle through a large 
artery called the aorta, goes throughout the tissues and 
returns to the right auricle. From this it passes into 
the right ventricle. It leaves the right ventricle through 
the large pulmonary artery, goes to the lungs and thence 
back to the left auricle (Fig. 48). From this it goes to 
the left ventricle and is ready for another circuit. As 
the circuit through the body is much longer than that 
through the lungs, the left ventricle exerts more pressure 
than the right ventricle and its walls are correspondingly 
thicker. 

(4) Elasticity. The blood vessels are extremely 
elastic. This quality causes the blood flow which in the 
arteries responds to the intermittent heart beat, to be- 
come steady by the time it reaches the capillaries. At 
every contraction of the ventricles blood is pushed into 
the two large arteries, which stretch to receive it. The 



CIRCULATION 



73 




Fig. 48.— Diagram of the circulation of the arterial and venous blood and the lymph. 
A.I., Arteries to head, arm and neck; V.pul., Pulmonary vein; L.Au., Left 
auricle ; Ao., Aorta ; L.v., Left ventricle ; A.2., Arteries to lower part of body; 
St., Stomach and intestine; Cap., Capillaries; L.d., Lymph duct; i., Luncs ; 
F.I., Veins from head, arms and neck ; v.c.Sup., Vena cava sup.; A .pul., Pul- 
monary artery ; R.au., Right auricle; R.v., Right ventricle ; Th.d., Thoracic 
duct ; v.c.Inf., Vena cava inf. (from lower part of body); Lac, Lacteals ; Liv., 
Liver; Ld., Lymph duct; F.2., Vein from intestine to liver (Portal vein); A.3., 
Artery to liver ; T.c, Tissue cells. (From Fitz.) 

recoil of their elastic walls makes them press upon the 
blood and squeeze it forward. But before they have 



74 PHYSIOLOGY 

squeezed it all out, the ventricles contract again and 
force in more blood, which again stretches them. Each 
new impulse sends in new blood, causing a succession of 
stretches in the artery as the column of blood passes 
on. This succession of stretches known as the pulse 
passes through the blood vessels much more rapidly 
than the blood itself. A heart beat is indicated by 
the beating of the artery on the wrist, for example, 
long before the blood forced out of the heart reaches 
there. As it is an accurate register of the heart beat 
it is useful to physicians in determining the rapidity of 
the heart beat. 

(5) Tone. — Tone is often confused with elasticity, 
but in reality it is something quite different. It in- 
volves a variation in the size of the arteries, but it de- 
pends not on the mechanical stretching of their walls by 
the entrance of blood, but upon the sustained activity 
of the muscles composing the walls through which the 
tubes may become large or small at any given moment. 

The walls of the arteries, especially the small ones, 
contain encircling muscle fibers ; if the fibers relax, the 
opening becomes larger and more blood passes through ; 
if they contract, the opening is smaller and less blood 
passes through (Fig. 49). 

The tone of the blood vessels is extremely important, 
because by means of it the system of tubes is kept com- 
pletely filled with fluid. If the blood vessels in the abdo- 
men should enlarge to their utmost, it would take all the 
blood in the body to fill them and the other blood vessels 
would be empty. This would mean a cessation of circu- 
lation. But the tone is regulated in such a way that thesQ 



CIKCTLATIOX 



75 



blood vessels do do< all enlarge al the same time, When 
certain blood vessels dilate, certain others contract, so 
that the volume of blood is B 

always slightly in excess 
of the capacity of the blood 
vessels. Elasticity is then 
called upon to make room 
for the excess. The sup- 
ply of blood sent to a tis- 
sue is thus adjusted to the 
need of the tissue. The 
more active the tissue the 
more the vessels dilate and 
the more blood passes 
through. The power of 
the vessels to change their 
size also has an important 
effect on the temperature 
of the body, as we shall see 
later. 

Composition of the 
Blood.— T he blood is 
largely composed of water. 
In it sodium chloride and 
other salts are dissolved. 
This salt solution holds in 
suspension several proteids 
and the red and white corpuscles. In it also are 
food for the tissues, secretions of various glands, and 
waste products of oxidation. Through the give and take 
of the tissues the food substances are present in the 




«-:~vn 



Fig. 49.— Diagram showing the relation 
between general arterial tone and the 
supply of blood to the brain. In A, 
the arterioles in organs m, 7?, s, are 
constricted, raising the general arte- 
rial pressure and forcing a large 
amount of blood through the brain. 
In jB, they are dilated, lowering the 
general arterial pressure and dimin- 
ishing the amount of blood sent to 
the brain. (After Hough and Sedg- 
wick.) 



76 



PHYSIOLOGY 



blood in fairly constant amounts. If through excessive 
eating an excess of proteid is received, it remains in 
the blood in the form of the blood proteids until it is 
given up to the tissues for use. If there is an excess 
of sugar, it is stored in the liver temporarily until there 
is a deficiency in the blood. If there is an excess of 
fat, it may be stored in any cell, but especially in the 
connective tissue cells, where it is apt to become perma- 
nent. If there is a deficiency of these substances in 




Fig. 50 A.— Coagulated blood highly magnified, a, Hed corpuscle much enlarged; 
&, Cross section of red corpuscle; c, Rouleau of red corpuscles; d, White cor- 
puscles; /, Fibrin. (From Fitz.) 



the blood the tissues themselves waste away and supply 
the lack. 

The Red Corpuscles. — Both red and white corpuscles 
are isolated living cells (Fig. 50). They resemble one- 
celled organisms, but they differ greatly from each other 



CIKCULATIOH 



77 




Fig. 50 B.— A white blood corpus- 
cle showing ameboid movement. 
(From Fitz.) 



in appearance and in work. Through a high-power lens 
the red corpuscles appear as flattened discs of a pale yel- 
lowish red. Their great number is responsible for the 
deep red color of the Mood. This color is due to a 

substance they contain called hemoglobin which has a 
remarkable affinity for oxygen. Oxygen passes from 
the air in the lungs into solu- 
tion in the blood, but the 
blood holds so little in solu- 
tion that the body would die 
for lack of oxygen were there 
not some way of storing it. 
Hemoglobin holds oxygen in 
a loose chemical combination 
and acts as a storehouse. By 
means of it the blood keeps on hand a sufficient supply 
of oxygen to maintain a steady flow into those cells which 
are deficient. 

Relation between Oxygen and Hemoglobin. — Oxy- 
gen never passes directly into the hemoglobin from the 
air in the lungs. It goes into solution first. While there, 
if it comes in contact with hemoglobin, a new substance 
called oxyhemoglobin is formed. This substance is 
extremely unstable. Oxygen and hemoglobin separate 
as readily as they unite and the oxygen goes into solu- 
tion, never directly to the tissues. Combination and 
separation take place at the same time in accordance 
with the relative amount of oxygen in solution and in 
combination with hemoglobin. If at any given place 
there is an excess of oxygen in solution very rapid pass- 
age will take place into the hemoglobin in that vicinity. 



78 PHYSIOLOGY 

If there is an excess in combination, the passage will be 
very rapid out of the hemoglobin. 

Oxygen Can Not Establish an Equilibrium. — Theo- 
retically an equilibrium tends to establish itself (1) 
between the oxygen in solution and that in combination 
with hemoglobin, (2) between the oxygen in solution and 
that in the air in the lungs, and (3) between the oxy- 
gen in solution and that in the cells ; but practically no 
equilibrium is possible in these cases because oxygen is 
continually passing out of solution into the cells where it 
is used and into the hemoglobin where it is stored. The 
pressure of oxygen is thus kept low in the solution, in 
response to which oxygen passes into the solution from 
the outside air. 

Origin and Fate of the Red Corpuscles. — The red 
corpuscles are formed in the red marrow of the bones 
and when very young they have a nucleus. As they 
mature they lose it, and in consequence they disintegrate 
very easily, usually in the spleen or in the liver. In 
high altitudes the rare air contains very little oxygen, 
but in compensation for its diminished flow into the 
blood the number of red corpuscles increases rapidly. 
As the amount of hemoglobin is increased, oxygen is 
removed from the solution faster than usual. It thus 
becomes more difficult to establish an equilibrium and 
the tissues have a better chance of getting from the 
rare atmosphere enough oxygen to maintain life. 

The White Corpuscles. — The white corpuscles are 
translucent, irregular in shape, and they have more than 
one nucleus. They resemble the ameba and like it they 
can move from place to place (Fig. 51). They work 



CIRCULATION 



79 



their way through the walls of the blood vessels and 
escape into the tissues, where they wander about doing 
valiant service for the body. They are very sensitive 
chemically. Wherever poisonous substances are pres- 
ent they gather in great numbers and by eating up 




From artery 



Fig. 51.— Migration of the white blood corpuscles from the capillaries of a frog in- 
to the tissues during inflammation. «, white corpuscle penetrating wall of capil- 
lary; b, white corpuscle in tissue; c, red corpuscle. (From Fitz, after Warren.) 

microbes and other foreign particles, they are often able 
to combat successfully severe disease. Matter from 
festered places is made up largely of these corpuscles. 

Coagulation. — The white corpuscles are also impor- 
tant because of their influence on the coagulation, or 
clotting, of blood. They contain an enzyme which has 
the power to hasten the physical process of coagulation so 
that it takes place at a much lower temperature than 
would otherwise be possible. 

When the corpuscle comes in contact with any foreign 
substance like dust or air the enzyme is rendered active. 



80 PHYSIOLOGY 

Through its activity fibrinogen, one of the proteids of the 
blood, is transformed into fibrin. As the change takes 
place, the small particles of the proteid which are held 
in suspension separate themselves from the liquid and 
assume a fibrous character. The fibers gather together 
in a larger and larger mass and in so doing enmesh the 
red corpuscles. These are in no way responsible for the 
process, for if the blood is whipped with a bunch of 
wires the fibrin may be obtained quite clear of them; 

The power of the blood to coagulate is of great service 
to the body, because in case of serious injury to a blood 
vessel, the contraction of its wall tends to close the 
wound and the coagulation of the blood prevents con- 
tinued bleeding. 

The Serum. — When the clot begins to form, the blood 
changes from a liquid to a red jelly; later the jelly con- 
tracts and forces out a yellow liquid. This liquid is 
the serum. It represents the blood with the fibrin and 
the red corpuscles removed. Under the influence of heat 
it also is able to coagulate because of the presence in it 
of proteids other than fibrin. Out of serum from the 
blood of horses is made the remedy used so wonder- 
fully in fighting diphtheria. 

A glance at the following table will show at once the 
relation of coagulated blood to the substances present in 
liquid blood. 



serum 



water 



. proteids >- plasma I 
Coagulated blood -{ } V liquid blood 

j fibrin J 

( corpuscles J 



clot 



CIRCULATION 81 

The Lymph. — The walls of the capillaries arc so thin 
that not only do the white corpuscles creep through, but 
by osmosis the plasma, or liquid portion of the blood 
with its dissolved substances, passes through. This 
liquid, now r called the lymph, is clear and colorless and 
contains everything in the blood except red corpuscles, 
which are too large to pass through the capillaries under 
ordinary conditions. The lymph bathes the tissues and 
keeps them moist. It brings the dissolved food mate- 
rials into such close contact with the tissues that they 
can without difficulty absorb what they need; and 
through the activity of the w T hite corpuscles, it removes 
wastes readily. 

The Lymphatics. — The lymph passes from the capil- 
laries into spaces between the cells. These spaces com- 
municate with each other, and into them open the ex- 
panded ends of small tubes, called lymphatics. The 
small lymphatics unite to form larger and larger tubes 
until two are formed (Fig. 48). These enter the two 
large veins near the neck, the larger or left one carrying 
the fats which were taken up by the lacteals, and pour 
the lymph into the blood through an opening protected 
by valves w T hich prevent the backward flow of the blood 
into the lymphatics. The lymph flows because of the 
pressure caused by muscular activity. There is no heart 
or pumping organ connected w T ith the lymphatic system 
in man; in the frog and certain other low T er animals, 
however, where the lymph spaces are very large, four 
rhythmically contracting organs called, lymph hearts 
force the lymph onward. 

Vaso-Motor Nerves. — Contraction and relaxation of 



82 PHYSIOLOGY 

the muscles in the walls of the blcod vessels are con- 
trolled by the vaso-motor nerves. These are very sen- 
sitive to changes of temperature. When a tissue is act- 
ive chemical changes take place which set free heat. 
This heat stimulates the vaso-motor nerves, the nerves 
convey the stimulus to the muscles in the walls of the 
blood vessels; the muscles relax, the vessels dilate, and 
more blood passes to the tissue. The blood brings food 
materials to replace the protoplasm that has split up, 
takes away the waste that has been formed in the 
process, and distributes the heat through the body. 
When the tissue becomes quiet less heat is set free, the 
nerves again convey a stimulus to the fibers, they con- 
tract and the supply of blood is decreased. The tone, 
or sustained activity, of the blood vessels is therefore 
very important not only because it aids the tissues 
to get the amount of blood they need when they 
need it, but because it helps to regulate the body tem- 
perature. 

Relation to the Body Temperature. — The tempera- 
ture of warm-blooded animals is self-regulating and 
constant, although chemical actions always taking place 
in the body are continually giving rise to heat. This 
continual setting free of heat would cause the tempera- 
ture of the body to increase were it not for the vaso- 
motor control of the blood vessels that go to the skin. 
As blood flowing through the skin is rapidly cooled 
through contact with the air, the amount of blood 
brought to the skin in a unit of time controls the amount 
of heat given off by the blood in a unit of time. 

The least variation in the amount of heat present in 



CIRCULATION 83 

the blood forms the stimulus Tor a corresponding varia- 
tion in the amount of blood broughl to the surface and 
consequently in the amount of heat given off. If the 
blood is too warm, the surface vessels dilate, more blood 
comes to the surface, and the skin becomes red. This 
is very noticeable after violent exercise or exposure 
to heat. The sweat glands are also stimulated to activ- 
ity, and perspiration occurs, which in evaporating takes 
heat from the body. If there is not enough heat in the 
blood the surface vessels contract. Blood is with- 
drawn from the surface and the skin appears white or 
purplish. 

Curiously enough these blood vessels are also very 
easily affected by the emotions. The face grows red 
or white under stress of shame, anger or fear. 

Interference with the Vaso-Motor Mechanism. — If 
there is any interference with the mechanism by which 
the giving off of heat is regulated, heat may be produced 
in the body by chemical action faster than it is given 
off by perspiration and the surface blood vessels. 
Fever results. We should therefore have some regard 
for the extreme sensitiveness of these blood vessels. If 
a draught strikes the body when the surface blood vessels 
are dilated they are forced to contract, the blood is with- 
drawn from the skin and the giving off of heat is inter- 
fered with at a critical moment. A cold, which is 
merely another name for fever, is apt to follow. Some 
of the important blood vessels are very near the surface 
in the wrists and in the ankles. In cold weather, then, 
the wrists and ankles should be covered. When the sur- 
face vessels are enlarged and full of blood, one feels 



84 PHYSIOLOGY 

warm ; if they are contracted, one feels cold. For this 
reason if there is little blood in the skin, one may feel 
cold even when the body is burning with fever. 

Effect of Alcohol on Body Temperature. — Alcohol 
prevents the surface blood vessels from responding 
readily to changes in temperature. A drunken man 
exposed to great cold is apt to freeze to death, for the 
relaxed surface blood vessels contain so large a quantity 
of blood that heat is given off much faster than it is 
produced. At the same time he may have a pleasure- 
able sensation of warmth because of the unusual amount 
of blood in the skin. 

Adaptation of the Circulation to Bodily Need. — Pos- 
sibly no other system has so many adaptations by which 
accidental defects correct themselves as the circulatory 
system. The clotting of the blood and the contraction of 
the vessels, which, following directly upon an injury, 
prevent bleeding to death, and the action of the surface 
blood vessels, which, through heat, are stimulated to 
cause the body to give off heat, and, through cold, are 
stimulated to cause the body to conserve its heat, have 
already been mentioned. In addition, we find that if 
the heart is stretched by an increased quantity of blood 
so that a harder beat than usual is necessary to force it 
out, the stretched muscle is able to beat harder than the 
unstretched muscle; if continued hard work is de- 
manded, the work itself strengthens the muscle. It 
grows thicker in response to the demand made upon it 
and it gains strength to meet the demand. If, however, 
too great a demand is made, as in the case of some 
athletes, the heart muscle becomes so thick that it can 



CIRCULATION 85 

not be supplied with nourishment and it loses its power 
to contract 

The rate of respiration is intimately connected with 
the rate of circulation, through the action of the vagus 
nerve, which is connected with both. If the respiration 
becomes slower and deeper, the heart beat becomes cor- 
respondingly quicker, so that the blood is kept moving 
fast enough to get sufficient oxygen for the body. 

If the pressure in the large arteries is lessened by the 
dilation of the smaller ones, the heart again works 
more quickly, blood is pushed faster into the large arte- 
ries, and the pressure is kept great enough to supply 
the tissues with blood. 

If the heart beats too fast, the extra pressure stimu- 
lates the depressor nerve and the beat is immediately 
decreased. 

Summary. — The blood is the great carrier of the body. 
It transports oxygen and digested food products to tis- 
sues deficient in them, and it carries the waste products 
of oxidation from the tissues to the excretory organs. 
It is a salt solution containing in suspension proteids 
and living corpuscles. The red corpuscles are important 
because they act as a storehouse for oxygen, and the 
white corpuscles are important because they help the 
body to resist disease and because they assist the clotting 
of the blood. 

The passage of the blood through the body is deter- 
mined by five mechanical features. The heart through 
its rhythmical beat furnishes the motive power. The 
valves force the blood to go in one direction only. The 
tubes to which the blood is confined are so arranged that 



86 PHYSIOLOGY 

the blood is forced to return to the heart after its pass- 
age through the body. The elastic walls of the arteries 
stretch to receive the blood and by pressing upon it 
force it to go onward in a steady stream. The tone, or 
the sustained activity of the muscles in the walls of the 
small arteries, regulates the capacity of the entire sys- 
tem, so that the tubes are always full of blood; it con- 
trols the amount of blood going to the tissues so that 
they always get the supply of oxygen and food that they 
need; and it keeps the body temperature constant. 



CHAPTER V 
REPRODUCTION 

Origin of Living Matter Unexplained. — Through a 

long series of slow changes the earth as it exists to-day 
was developed from a kind of nebula, and complex 
organisms that live upon the earth were evolved from 
very simple organisms. We do not understand how the 
nebula or non-living matter first came into existence, 
and we do not understand where and how the first living 
form originated. It seems but a step from non-living 
matter to the simplest form of living matter, yet it is 
a step that marks a sharp distinction and we do not 
know how it was taken. Some day perhaps we may 
bridge the gap in our knowledge and find out how the 
peculiar combination of non-living elements called 
protoplasm became endowed with life, but to-day we 
must content ourselves with the knowledge that the 
subtle thing that we call life transfigures the mass of 
elements and gives it a threefold power to move, to 
grow, and to reproduce, and so distinguishes it abso- 
lutely from all forms of non-living matter. 

Reproduction. — Living matter is able to manufacture 
new substances like itself from food that it assimilates. 
Living organisms in consequence grow and when they 
reach maturity they produce out of the extra protoplasm 

87 



88 



PHYSIOLOGY 



that they make new organisms like themselves. This 
power is called reproduction. It belongs to all organ- 
isms alike. In one-celled animals the process is of 
course very simple, but it does not differ very widely 
in its essentials from the process as it exists in higher 
animals. 

In One-Celled Animals. — The simplest form of the 
process is called fission. A one-celled organism splits 



mac 




mac 




~mtc 



Fig. 52.— Paramecium. A, Fissicn; B, Conjugation. (From Sedgwick and Wilson, 
after Calkins.) m, mouth ; mac, mxc, nucleus. 

into two and in place of the single individual there are 
two half-sized individuals. These grow and the process 
is repeated. After a time the animals seem to lose their 
vigor and are unable to divide unless the protoplasm is 
rejuvenated. This is accomplished through a process 
called conjugation. Two animals apparently alike come 



REPRODUCTION 89 

close together and the protoplasm, or the nucleus, of the 
one passes into the protoplasm of the other. The fusion 
that follows gives the cells an increased impetus toward 
division and the necessary strength for it (Fig, 52). 

In Many-Celled Animals. — Conjugation is not unlike 
the process of fertilization that occurs in human beings 
and other many-celled animals. In this process two 
dissimilar cells unite, and the union results in the 
formation of a new cell with the power to divide and 
form other cells. In many-celled animals the cells do 
not split entirely apart when they divide but remain 
attached to each other. Soon they become differentiated, 
that is they grow different in form and function, and 
finally an animal like the parent is formed. Complete 
separation, however, occurs in certain worms where an 
animal may split into two new animals, and also in 
those organisms which are able to form a new individual 
from a bud or cut off portion. 

Restricted to Special Cells. — In one-celled organisms 
any cell may by fission produce a new organism like 
the parent. In many-celled organisms any cell may 
divide, but the power to form a new individual like 
the parent is restricted to certain undifferentiated cells 
called the reproductive cells. This is necessarily true, 
for when a cell divides after differentiation the new 
cell is differentiated in the same way; but if a simple 
undifferentiated cell divides, the new cells retain the 
power of differentiation and are able to give rise to the 
various tissues of the new organism. 

Reproductive Cells of the Sea-Urchin. — Reproduc- 
tion in a many-celled animal like the sea-urchin is very 



90 



PHYSIOLOGY 



simple. These animals live in the water (Fig. 53). At 
certain seasons of the year primitive, or undifferenti- 




Fig. 53 A.— Sea-urchin. 



ated, cells multiply in their bodies in great numbers. 
These cells are formed by special reproductive organs 





Fig. 53 B.— Sea-urchin with spines removed. 

which open to the outside by a tube or duct. The organs 
are of two kinds and are found in different individuals 



REPRODUCTION 



01 



called the male and the female. They give rise to cells, 
which differ from each oilier very definitely. Those 
formed in the female are large, round and have no power 

of themselves to move. They are called egg cells, or ova. 
The organ in which they are formed is the ovary. In the 
male the cells are small, irregularly shaped and motile 
(Fig. 54). They are called sper- 
matozoa, or sperm cells, and the organ 
in which they are formed is the 
spermary. 

Attraction of the Sexual Cells. — 
The egg cells have a chemical attrac- 
tion for the sperm cells. By vibrat- 
ing the long tail-like appendage, the 
sperm cells move through the water 
and approach the egg cells. One of 
them punctures the w 7 all of an egg 
cell, and its nucleus, with the slight 
amount of protoplasm surrounding 
it, enters. The tail is left outside and 
finally disintegrates. A single cell 
then remains, containing two nuclei, 
one belonging to itself, the other to a 
cell of different character. These 
nuclei fuse. The large cell with now 
but a single nucleus has, like the one-celled animal after 
conjugation, a new and increased pow T er of division. 

Division of the Fertilized Egg. — It divides very 
rapidly first into two cells, which remain attached to 
each other, then into four, eight, sixteen, thirty-two 
cells and so on, until a mass like a mulberry is formed 



Fig. 54. — Spermatozoa. 
A % of the nigh thaw i; ; 
J3, of the green frog; 
n, nucleus; m, middle 
piece; s, tail. (After 
Hertwig.) 



92 



PHYSIOLOGY 



(Fig. 55). All of these cells have a marked affinity for 
oxygen. Those on the inside therefore push their way 




Fig. 55. — a, egg cell; b,c,d,ef, successive 
Wilson.) 



of division. (From Sedgwick and 



to the outside toward the oxygen. In this way they 

become arranged in a hollow sphere called a blastula 

(Fig. 56). As these cells have 
their affinity for oxygen satisfied, 
some of them develop a new affin- 
ity. They are attracted toward 
other cells and move inward until 
a pear-shaped structure called a 
gastrula (Fig. 57) is formed, 
which has a wall composed of two 

layers of cells and an opening leading from the central 

cavity to the outside. 

Differentiation of Cells. — The two layers of cells are 




Fig. 56. — Diagram of a 
blastula. 



REPRODUCTION 



93 



now exposed to very differenl conditions; in consequence 
they assume differenl characteristics. The cells in the 

outer layer, in contact with sea water, become more or 




Fig. 57.— Diagram of a gastrula. 



less hardened and assume a protective function. Those 
on the inside assume a nutritive function. We thus 
have formed two primitive layers called the ectoderm 
and the entoderm. As the cells increase in number 
a new layer called the mesoderm is formed between 
them. These are the three primary layers. From them 
all the tissues of the adult organism are formed. The 
higher the animal the more marked the power of cellular 
differentiation, and the more highly developed the re- 
sulting tissues. From the ectoderm all protective organs 
are formed, skin, nervous system, sense organs ; out of 
the entoderm, all organs which have to do with alimenta- 
tion, the alimentary canal, the liver, pancreas, lungs ; 



94 PHYSIOLOGY 

out of the mesoderm, everything else, — bones, muscles, 
blood, connective tissue, glands. 

The Process Universal. — The development of the sea- 
urchin up to the gastrula is typical. The main changes 
that have been described as taking place during fertiliza- 
tion, cleavage of the egg, and formation of the first two 
germ layers occur in all multi-cellular animals. Each 
particular group of animals, however, has its own 
peculiarities of development resulting from variations 
in environment or structure. Some animals like the 
hydra never pass beyond the gastrula stage. Others 
more highly developed pass through all of the stages of 
their immediate ancestry. In other words, " the history 
of the individual repeats the history of the race." This 
fact is one of the strongest arguments in favor of the 
theory of evolution; it seems to justify the assumption 
of a common ancestry, and belief in the evolution of 
complex from simple forms. 

Protection of the Cells in Land Animals. — In land 
animals egg cells and spermatozoa can not be turned 
loose because their delicate outer walls would dry in the 
air and the cells w T ould die. Some way must therefore 
exist by which the sperm cell may reach the egg cell 
without danger of the death of either one. The cells 
reach the exterior of the sea-urchin through tubes that 
lead from the organs where the cells are formed to the 
outside. These tubes are moist. In land animals the 
cells come in contact with each other without exposure 
to the air in one of the tubes. 

As the egg cell can not move and the sperm cell can 
move, the sperm cell passes over to the tube containing 



REPRODUCTION 95 

the egg cell. The two unite in the tube and the egg 
gains the power of division and differentiation. In in- 
sects, birds, reptiles, after the process of fertilization oc- 
curs, a hard outer wall forms around the eggs. They 
can then be exposed to the air without injury. The 
process of differentiation and growth continues within 
the shell until the young animal can take care of itself, 
when it is hatched. In higher animals, w T here a hard 
shell does not form, the egg can not be exposed to the air 
until it is so protected that no harm will result. There- 
fore, the length of time that the fertilized egg remains 
in the tube and the amount of development which takes 
place there depend upon the degree of development which 
is necessary for the protection of the new individual. 
In the case of human beings the new individual must 
be completely formed before it leaves the tube. 

Sexual Reproduction of Plants. — In plants the proc- 
ess is essentially the same. The ultimate end and aim 
of all organisms seems to be the reproduction of their 
own kind ; the flower is not made to please our eyes but 
to aid in the production of a new plant. The brightly 
colored floral envelopes usually present surround the 
more important stamens and pistils (Fig. 58). These 
may, or may not, appear in the same flower. The pistil 
is a tube (the style), with a basal enlargement (the 
ovary) and a flaring end (the stigma). In the ovary, as 
the name indicates, the ovules, or egg cells, are formed. 
Each of these may be compared to a female sea-urchin, 
for it forms within itself a little egg cell which must 
be fertilized if it is to develop into a new individual. 



96 PHYSIOLOGY 

The stamen is a long filament with an anther at the top. 
The anther gives rise to the pollen grains. These grains 
are so tiny that they are easily blown about by the wind 





Fig. 53.— Flower showing stamens and pistil. 

to fall perhaps on the sticky surface of the stigma. 
Each little pollen grain may be compared to the male 
sea-urchin, for it forms within itself a sperm cell. 

The sperm cell, like that of the sea-urchin, is irregu- 
larly shaped and develops a tail. The tail is of no use 
for swimming because it is not surrounded by water and 
it is held fast by the sticky surface of the stigma ; but by 
means of it the nucleus of the sperm cell reaches the egg 
cell. The tail, or pollen tube, grows longer and longer 
until it reaches down the style to the ovary ; the nucleus 
of the cell then works its way down through the tube, 
punctures and enters the egg cell and unites with the 
nucleus which it finds there (Fig. 59). This is the 
process of fertilization. The new cell, like the fertilized 



REPRODUCTION 97 

egg of the sea urchin, can now divide and the new cells 
can differentiate. The process of differentiation con- 
tinues until a tiny new plant called a seed is formed. 




Fig. 59.— Diagrammatic section of a flower, showing a pollen grain sending a pollen 
tube down to the ovule. C, calyx; Co, corolla; a, anther, and /, filament, of 
the stamen ; O s ovary surmounted by s t style, and st, stigma; p, pollen grains, 
some in the anther, others on the stigma; iV", ovule ; E, germ cell ; pt, pollen tube 
penetrating the style and reaching the germ cell through an opening (the 
micropyle; into the ovule. 



Under proper conditions this is able to unfold itself 
into a plant like the parent. 

Summary. — Reproduction may be non-sexual or 
sexual. In non-sexual reproduction a cell, or a collec- 
tion of cells, breaks away from the parent and develops 
into a new organism. There is no union of cells. In 
sexual reproduction two cells unite to form a new cell 
which has the power to divide and differentiate. In 
one-celled forms the uniting cells are similar and we call 
the process conjugation. In higher forms the cells are 



98 PHYSIOLOGY 

dissimilar and we call the process fertilization. The two 
cells are usually formed in different individuals, though 
they may be formed in the same individual. The egg 
cell is large, round, quiet ; the sperm cell is small, irregu- 
lar, motile. In aquatic forms the cells pass into the 
water and unite there, but in animals that live on land 
the union takes place in the tube leading from the ovary 
to the outside. The egg becomes better and better pro- 
tected as development becomes more complex; finally it 
remains in the body until the whole development has 
taken place. 



CHAPTER VI 
IRRITABILITY 

Protoplasmic Motion. — Living matter is irritable; 
that is, it has the power to move in response to a stimu- 
lus. The character of the motion varies. Sometimes 
the protoplasm circulates within the cell. This flowing 
movement aids in the distribution of nutritive sub- 
stances to all parts of the cell and in the concentration 
of wastes. It may also bring about the movement of the 
cell from place to place. The ameba and the white blood 
corpuscles, for example, creep slowly along in the direc- 
tion in which the protoplasm flows (Figs. 16, 50 B). 

Ciliary Motion. — Sometimes the cells have hair-like 
projections from their surface which move to and fro. 
By the concerted movement of these cilia a free cell 
easily moves from place to place like a boat propelled 
by oars (Fig. 2). If the ciliated cells form the surface 
of a membrane like that covering the gills, or lining the 
oesophagus, of many animals, the moving of the cilia pro- 
duces a current which, passing over the surface of the 
membrane, carries along any substances contained in 
the liquid that bathes it. 

Muscular Contraction. — In many-celled animals some 
cells have been so differentiated that they are able to 
change their form by contracting and relaxing. These 

99 



100 



PHYSIOLOGY 




are called muscle cells (Fig. 
long and slender and they ar 
such a way that when 
or the muscle as a whole, 
each cell grows shorter 
grows correspondingly 
the effort of the indi- 
Through the activity of 
able to change its form 
place. 

Theory of Muscular 
theories have been ad- 
muscle cell contracts but 
With the aid of a com- 
tain definite changes 
place in the structure of 
tion. These may be 



60). They are usually 
e arranged in groups in 
they contract, the group, 
contracts (Fig. 61). As 
and thicker, the muscle 
shorter and thicker and 
vidual cell is magnified, 
these cells an animal is 
and move from place to 

Contraction. — Various 
vanced to explain how a 
they are not satisfactory, 
pound microscope, cer- 
may be seen to take 
the cells during contrac- 
accounted for by the 



B 



C 



P 



w 



Fig. 60.— Muscle cells. A, cross section from intestine of a dog ; J3, isolated cell 
from intestine of a rabbit; (7, part of a single fiber of voluntary muscle from 
the leg of a rabbit ; p, protoplasm ; n y nucleus. (From Sedgwick and Wilson, 
after Ranvier.) 

theory that when protoplasm disintegrates, as it always 
does during activity, the resulting heat causes the pas- 



IRRITABILITY 



101 




sage of a fluid from one part of the cell to another part 
so thai its shape is changed. This would be a satis- 
factory explanation were it not for the fact that an ap- 
preciable time is necessary for the passage of the fluid, 
and the muscles in the wings of 
insects move far too fast to per- 
mit it to occur. 

Stimuli. — A muscle contracts 
in response to some outside 
stimulus. This stimulus may be 
physical, e.g. a blow, or a change 
of temperature ; or chemical, e.g. 
an acid or other irritating sub- 
stance. Some muscles seem to 
work automatically without the 
intervention of an outside stim- 
ulus, but their spontaneity is 
only apparent. They are really 
stimulated by some substance 
present in the blood. The heart 
is probably the most remark- 
able of these muscles, for it con- 
tracts rhythmically as long as there is life, and so long 
as it is provided with adequate nourishment it seems 
to thrive under the constant work. 

Rhythmical Contraction. — Muscles which normally 
do not show r rhythmical contraction will contract rhyth- 
mically if excised and placed in a balanced solution of 
sodium chloride and calcium chloride. These salts are 
present in the blood in such proportion that the blood 
is the balanced solution for the heart muscle. So long 



Fig. 61— Diagram showing ar- 
rangement of muscle fibers in 
relation to their tendons. A, 
in muscles contracting 
through a considerable dis- 
tance; B, in muscles of shorter 
and more powerful contrac- 
tion; C, in muscles of very 
short and powerful contrac- 
tion. (From Fitz.) 



102 PHYSIOLOGY 

as it is bathed by the blood then, and its chemical consti- 
tution remains unchanged, the heart will continue its 
contractions indefinitely. 

The excess of carbon dioxide that occurs at regular 
intervals in the blood is possibly the stimulus which 
incites the respiratory muscles to rhythmical activity. 

The movement of the muscles in the wall of the ali- 
mentary canal by which the contents of the canal are con- 
tinually urged onward is also apparently spontaneous, 
but the presence of any foreign substance in the intes- 
tines stimulates its muscular walls to activity. The 
presence of the food then is an exciting cause. 

Influence of the Structure of Muscles. — The impor- 
tant thing about the muscles is that through their 
contraction they bring about the complex movements of 
higher organisms. Each muscle is capable of a single 
movement. It changes its shape in accordance with the 
arrangement of its fibers, or cells, which grow shorter 
during contraction. In the muscle that bends the arm, 
the fibers lie side by side so that when they contract 
the muscle grows shorter, but in the diaphragm they 
are the radii of a circle and when they contract the 
circle grows smaller. 

Influence of Arrangement of Muscles. — Complex 
movements are produced by the co-operative activity of 
a number of muscles. The character of the movement 
depends upon the shape and the arrangement of the mus- 
cles in the body of the animal. In an earthworm one set 
of muscles runs lengthwise and another encircles the 
animal. By the alternate contraction of the two sets 
the worm creeps over the ground. In a sea anemone the 



IRRITABILITY 103 

body is cylindrical and the muscles run lengthwise. 
When they contract they pull the animal back againsl 

the rock to which it is attached. 

The number, shape and arrangement of muscles vary 
greatly in different animals. In simple animals they 
are few in number, they are arranged very simply, and 
few movements are possible. In higher animals they 
are numerous and they vary greatly in size, shape and 
arrangement. An infinite variety of movements may 
therefore be produced by their contraction. 

The Function of a Skeleton. — Very simple animals 
are more or less jelly-like and formless. In larger and 
more complex animals the soft tissue is supported in 
order that the shape of the body may be maintained and 
the necessary resistance furnished for complex move- 
ments. The food that they eat contains earthy matter 
which is built in the body into a strong resistant sub- 
stance firm enough to form a support. The softer parts 
of the body thus become protected by the development 
of a skeleton. 

The Skeleton External in Lower Animals. — In lower 
animals the skeleton is on the outside of the body, but 
it must not be regarded as a house which the animal 
enters or leaves as it likes. It is an integral part of the 
animal. In oysters and clams the body lies inside a shell 
made of two pieces which may be opened or closed by the 
activity of strong muscles attached to it. In starfish, 
lobsters and insects the connection is closer. The en- 
closing shell is jointed and the muscles are so intimately 
connected with it that every movement involves a move- 
ment of the shell. 



104 PHYSIOLOGY 

Internal in Higher Animals. — In higher animals the 
skeleton is internal. It is entirely covered by muscles 
and its bones are so arranged that they move easily 
when the muscles associated with them contract. There 
are in man a great many. bones (208) of varied shape 
and size, usually described as long, short, flat or irregu- 
lar. Except in the head, the hip, and the lower part of 
the spine where the bones are fused or sutured, a joint 
permitting more or less motion is formed wherever two 
bones come together. The separate bones at the joint 
are held in place by strong ligaments of fibrous, in- 
elastic tissue. They slip over each other easily and 
smoothly because the surfaces that come in contact are 
covered with smooth cartilage that is constantly kept 
moist with fluid. 

The Structure of Bones. — The bones are composed of 
living animal matter, water, and earthy matter mostly 
salts of lime. They are rigid, strong and light. The 
large bones attain the necessary size without too 
much weight by becoming hollow or by developing 
spongy bone inside. The number, the shape of the 
bones, the wonderful w 7 ay in which they are fitted to- 
gether, their strength and lightness insure the ease and 
quickness w 7 ith w r hich we are able to move. 

The Spinal Column. — The fundamental part of the 
human skeleton is the spinal column, or backbone, which 
is so constructed that it combines the greatest strength 
with the greatest flexibility. The separate bones of 
which it is composed may be felt through the skin. 
They vary in form according to their situation, and in 
consequence they vary in the amount of motion that they 
are able to make. In the neck, for example, there is 



IKKITAHILITY 



much more freedom than there is in the trunk. Move- 
ment between any two vertebrae is restricted by the unit- 
ing ligaments, but there are so 
many vertebrae that though each 
one moves but slightly, the column 
as a whole is capable of bending 
considerably (Fig. 62). 

The Shoulder Girdle.— About 
the spinal column as an axis the 
other bones are arranged so that 
the body has a two-sided symmetry. 
It is surmounted by the head and 
to it are attached two bony girdles 
each of which carries a set of ap- 
pendages (Fig. 63). The shoul- 
der girdle consists of two shoulder 
blades which lie one on each side 
of the back, two collar bones which 
lie at the base of the neck in front, 
and the breast bone to which the 
collar bones are attached. The 
upper end of the arm bone fits into 
a shallow cup at the upper outer 
end of the shoulder blade. 

The Pelvic Girdle.— The pelvic 
girdle consists of two broad flaring 
bones joined together by ligaments 
in front and united to the spine by 
ligaments in the back. The upper FlG - 62.-Side view of the 

spinal column. (From 

end of the leg bones fits into a hollow. Martin.) 

The Ribs, — The ribs encircle the body and enclose 



106 



PHYSIOLOGY 



the heart and lungs. They are united to the vertebra 
behind and to the breast bone in front and furnish sup- 




Fig. 63.— The skeleton of the trunk seen from the front, showing the shoulder girdle 
composed of the collar bone ((7) and the scapula (£), and the pelvic girdle com- 
posed of the sacrum and the innominate hones (Oc). (From Martin.) 

port for the shoulder girdle and the arm muscles. As 
they are not rigidly fastened they are capable of move- 
ment which aids breathing (Fig. 64). 

Appendages. — The legs and arms are each divided 



IRRITABILITY 



107 




Fig. 64. -The ribs of the left side, with the dorsal and two lumbar vertebra?, the 
rib cartilages and the sternum. (From Martin.) 

into an upper part, consisting of a single large bone, and 
a lower part, consisting of two bones placed side by side 
that turn on each other. A number of small bones con- 



108 



PHYSIOLOGY 




p 




6 



Fig. 65.— Bones of arm and leg. Fe, femur; Fi, fibula; H, humerus; P, patella ; 
R, radius; T, tibia; U, ulna. (From Martin.) 

nect these with the bones of the hand and foot, which 
are each made of five slender bones. The first of these 
five is tipped with two small bones and the others 



IRRITABILITY 



109 



each with three small bones, for the fingers and toes 
(Fig. 65). 

Joints. — Wherever two bones come together to form a 
joint, the one nearest the center of the body acts as a 
support for the motion of the other one. At the shoul- 
der, for example, the upper arm moves, the shoulder 
remains quiet; at the elbow the lower arm moves, the 




Fig. 66.-^4, lengthening of biceps when arm i9 extended; C, clavicle ; S, scapula; 
Sh, short head of biceps ; Lh, long head ; B, biceps. (From Fitz.) B, con- 
traction of biceps to flex arm; S, scapula; B, biceps; 7*, tendon; H, humerus; 
U, ulna; i?, radius. (From Fitz.) 

upper arm is quiet; at the wrist the hand moves, the 
lower arm is quiet. There is an advantage in this, 
for it insures quickness and ease of movement for the 
extremities. 



110 PHYSIOLOGY 

Relation of Muscles to Bones. — Bones have no power 
of themselves to move. Their movement is entirely due 
to the contraction of muscles that are attached to them 
(Fig. 66). An infinite variety of movement is possible 
through the co-ordinated activity of a great number of 
muscles. These vary greatly in shape and size and 
are arranged about the skeleton in such a way that 
the beautiful symmetry of the body is maintained and 
the greatest amount of work accomplished with the least 
expenditure of energy. 

If we feel the muscles through the skin when they 
contract we may notice that the active muscle is fre- 
quently situated some distance from the point of motion. 
The muscles that move the upper arm are situated on the 
trunk, those that move the lower arm are situated on the 
upper arm and those that move the fingers are situated 
close to the elbow. The weight of the muscle thus rests 
on the stationary bone and the other bone is free to 
move. The muscles are fastened to the bones by inelas- 
tic tendons that are sometimes very long. The tendons 
economize space and slip easily over the moving joint. 

The muscles are arranged about a joint so that its 
motion is perfectly controlled ; the number depends upon 
the character of the joint and the character of its work. 
In the shoulder where a ball and socket permit rotary 
motion there are a large number of muscles, but in 
hinge joints which merely permit flexion and extension, 
only two controlling muscles are necessary though in 
powerful action these may be reinforced by others. 

Movement is always due to contraction, not to relaxa- 
tion. Usually muscles are arranged in antagonistic pairs 



IRRITABILITY 



111 



so associated that it' one contracts the other relaxes. On 
each side of a hinge joint is a muscle attached to both 
bones; one bends the joint when it contracts, the other 
straightens the joint when it contracts. In moving the 
eve to the right, the outside muscle of the right eye con- 
tracts while the inside muscle relaxes (Fig. 67). At 




Fig. 67.— The eye and its muscles, a, pulley of upper rotating muscle ; b, part of 
skull (eye socket); c, muscle of upper lid; d, upper rotating muscle ; e, muscle 
turning eye upward; /, muscle turning eye outward; ^, muscle turning eye 
downward; h, bone of socket ; i, optic nerve; Jc, lower rotating muscle. (From 
Fitz.) 

the same time, the inside muscle of the left eye contracts 
while the outside muscle relaxes. Both eyes thus move 
together. 

Relation of Nerves to Muscles. — If the finger touches 
a hot stove, the muscle that jerks it away is likely 
to be one of those in the upper arm. This muscle 
did not come in contact with the stove, yet the stimulus 
reached it. There must therefore be a j:>assageway by 
which a stimulus applied to the skin can reach a muscle 
far removed from the point of contact. This connecting 
passageway is furnished by the nerves. 



112 



PHYSIOLOGY 




Structure of the Nervous System. — A nerve is made 
of fibers that are prolongations of large irregular cells 
(Fig. 68). Like the circulatory 
system, the arrangement of the 
nerves depends on the shape, size 
and development of the animal. 
In the starfish, for example (Fig. 
69), it is star-shaped, for a ring 
around the mouth sends a branch 
to each ray. 

There are always one or more 
central masses of cells from which 
the fibers radiate. In worms and 
lobsters these masses of cells are 
arranged at intervals along a cord 
that extends the entire length of 
the body (Fig. 70). This is the 
prototype of the spinal cord of 
human beings. The spinal cord 
is the fundamental part of the 
vertebrate nervous system. It is 
situated in a canal formed by the 
vertebrae where it is thoroughly 
protected. From this cord nerves 
are given off at regular intervals. 
These subdivide into smaller and 
smaller nerves which go to every 
part of the body. At the anterior, 
or head end, of the cord the cells 
are massed into a large organ called the brain which 
also gives off nerves in the same way. These go to 




Fig. 68.— Diagram of a mo- 
tor nerve cell. CL, motor 
nerve cell of spinal cord; 
A., axis cylinder; C, col- 
lateral branch ; Ms. , me- 
dullary sheath ; iV, node ; 
T 7 ., terminal branches ; 
M., muscle. (From Fitz.) 



IEKITABILITY 113 

the face and the various parts of the sense organs 

(Fig. 71.) 

The Work of Nerves. — The nerves form the only 
protoplasmic connection between the skin and various 




Fig. G9.— Diagram of the nervous system Fig. 70.— Diagram of the 

of a starfish nervous system of an 

earthworm. 

muscles. When a nerve ending in the skin is stimulated 
by some form of physical or chemical contact, the stimu- 
lus passes down the nerve and gives rise to a sensation, or 
to the contraction of a muscle, or to both. A sensory 
nerve carries a stimulus to the ventral or front side of 
the spinal cord. From there it may pass through the 
spinal cord to the brain and give rise to a sensation ; and 
it may also pass to the dorsal side of the spinal cord 
and back to the muscles through a motor nerve and give 
rise to a contraction. Sometimes the passage is so quick 
from the point of contact to the muscle that the stimulus 
does not have time to go to the brain first. The move- 
ment then takes place before the mind knows anything 



114 



PHYSIOLOGY 




about it. We can neither 
aid nor interfere with it. 
This is called a reflex 
movement. 

The Value of the 
Nerves. — The value of the 
nerves to the body lies in 
their extreme sensitiveness 
and. in the rapidity with 
which a stimulus passes 
through them. Many ex- 
periments have been 
tried with lower animals 
to ascertain whether nerves 
are responsible for their 
various reactions or 
whether the reactions are 
dependent upon muscles. 
By removing the nerves 
from these animals so that 
they can play no possible 
part and by stimulating 
the muscles directly, it 
was found in every case 
that the animal showed its 
usual reaction and that 
this reaction depended 

Fig. 71.— Diagrammatic front view of the spinal cord and bulb, showing spinal 
nerves, one side chain of sympathetic ganglia, and some of cranial nerves. 
Ce.p., cervical plexus ; s.s., branch to sympathetic system ; B?\p., brachial 
plexus; S.g., sympathetic ganglia; L.p., lumbar plexus; S.c, sciatic nerve ; 
S.p.i sacral plexus ; C.p., coccygeal plexus. (From Fitz.) 



IRRITABILITY 115 

upon the structure and arrangemenl of the muscles. 

But it was always found that the reaction was very, 
very slow in following the stimulation. This means 
that if the animal had to depend on the direct stimula- 
tion of the muscle its life would be in danger because 
the reaction could not come quickly enough. When 
animals as highly developed as dogs are deprived of the 
use of the nerves, they are kept alive with a great deal 
of difficulty because of the slowness with which the body 
responds to changes in temperature. 

These experiments show that human beings are utterly 
dependent upon the nervous system, for without the 
nerves the muscles would respond to stimulation too 
slowly to maintain life. But while we recognize the 
importance of the nerves we must realize wherein it lies. 
They are in no sense responsible for movements. This 
is the work of the muscles. They cannot initiate a move- 
ment. This is the result of a stimulus. But they are 
extremely sensitive and they conduct a stimulus with 
wonderful rapidity. They are therefore effective as con- 
ductors of stimuli. 

Sense Organs. — All nerves are sensitive to chemical 
and physical stimuli, but nerves connected with the 
special senses are especially adapted to particular 
stimuli. The most widely distributed of the senses is 
that of touch, or sensitiveness to physical contact with 
external objects. It is found in all animals and it is 
generally distributed over the whole body. The other 
senses are restricted to special areas on the body and, 
in their complete development, to higher animals. The 
taste nerves are stimulated by substances in solution. 



116 PHYSIOLOGY 

and the olfactory nerves by volatile substances. The 
one is distributed over the tongue in higher animals 
and the other over the upper part of the nose cavity. 
To what extent the lower animals possess these senses is 
a question. They can certainly distinguish substances 
that please them for food and they frequently make 
their way unerringly to food from a distance, but it is 
not probable that they smell and taste consciously as 
we do. 

The nerves stimulated by vibrations are perhaps the 
most sensitive of all. The optic nerve which is respon- 
sible for sight is stimulated by ether vibrations; the 
auditory nerve by means of which we hear, by air vibra- 
tions. Some of the lower animals have rudimentary 
organs sensitive to sound and light but they have no 
eyes that can distinguish form as do ours and no ears 
that hear as do ours. The human eye is marvelously 
developed. Like a photographer's camera it reproduces 
an image on the sensitive surface of the retina and the 
impression of form and color is conveyed to the brain 
by the optic nerve. 

Sympathetic System. — Many of the spinal nerves are 
connected with a chain of ganglia which lie in two rows 
on the ventral side of the spinal column. The ganglia 
and the nerves that are given off from them form what is 
called the sympathetic nervous system (Fig. 71). It is 
so called because it is extremely sensitive to the condition 
of the body. Through it the organs are adjusted auto- 
matically to their needs and to the demands made upon 
them. If food is present in the stomach its glands are 
stimulated to activity. If the blood pressure falls the 



IRRITABILITY 117 

licari is stimulated to beal faster, if il rises, to beat more 
slowly. If a muscle is active the blood vessels that go 
to it are stimulated. They enlarge and carry more 
blood to it. After violent exercise when a great deal 
of heal has been set free by the activity of the muscles 
the surface blood vessels in the skin are stimulated and 
they enlarge. Also the sweat glands are stimulated to 
activity and an increase in perspiration follows. If the 
skin loses heat through sudden or prolonged constriction 
of the surface blood vessels one is apt to feel cold and 
shiver. Shivering is a spasmodic contraction of the 
muscles. The heat thus produced compensates for that 
which has been lost and tends to produce a feeling of 
warmth. 

Exercise. — Exercise is an important factor in the 
health of the body. It is a natural form of massage. 
It involves the disintegration and reformation of pro- 
toplasm, the kneading of the blood vessels, a quicker 
heart action and deeper respiration. Thus it facilitates 
the intake of oxygen and the carrying off of waste 
products. It must, how T ever, be of the proper sort and 
must be taken in moderation, and with due regard for 
times and seasons. Exercise should not be taken too 
soon after eating because the blood circulates rapidly 
through the exercised parts, the blood vessels there be- 
come enlarged and draw blood away from the stomach 
where it is due at that time. 

Curiously enough either too much exercise or too 
little has exactly the same effect — a lack of oxidation. 
In both cases disintegration of complex substances 
in the muscle takes place in excess and oxygen is 



118 PHYSIOLOGY 

not supplied fast enough to oxidize the resulting 
products. 

If too much exercise is taken habitually as often hap- 
pens in the case of athletes, the effects may be disastrous. 
When a muscle is properly exercised it increases in 
size, if it is well nourished and well aerated it becomes 
stronger and better able to work. This is true of the 
heart as of every other muscle. 

The blood that passes through the heart at every 
beat does not come intimately enough in contact with 
the tissue of the heart to furnish the necessary nour- 
ishment. This is brought by the coronary artery which 
permeates its tissue. If too great demand is made on 
the heart, the heart muscle becomes so thickened that 
the coronary artery can not supply sufficient nourish- 
ment, the muscle then degenerates and loses the power 
to contract. 

The development of the athlete is not always towards 
perfection. Where one set of muscles is used to the 
exclusion of another set, the first becomes over-developed 
at the expense of the latter. The result is the very dis- 
agreeable condition that is called muscle-bound. 

Effect of Alcohol on the Nervous System. — Indul- 
gence in alcoholic drinks has a decidedly deleterious 
effect on the nervous system. 

Alcohol apparently stimulates the body and mind to 
greater activity and it is taken frequently for its ex- 
hilarating effect. In reality instead of stimulating the 
brain to work more clearly it acts like a narcotic and 
inhibits the activity of the restraining influences of 
the will and of habit. This inhibition results at first 



IRRITABILITY 119 

in a throwing off of conventionality so that a person 
may do things which in a normal moment seem impos- 
sible because of the influence of habit. If larger quan- 
tities are taken, all strength is inhibited and we firid 
the peculiar vagaries of the .drunken man. Control of 
mind and body is lost ; speech becomes thick and unin- 
telligible ; muscular action becomes loose and ineffective ; 
and in addition to the loss of voluntary control, involun- 
tary physical control is lost. 

Alcoholic indulgence is particularly bad for young 
people because it stunts growth and because the danger 
of forming the habit is infinitely greater before the 
age of thirty than it is afterwards. 

Summary. — Irritability manifests itself in the cir- 
culation of protoplasm within the cell, in ciliary motion, 
and in muscular activity. In higher animals the move- 
ments of the body are due to muscular contraction. 
The contraction takes place in response to an outside 
stimulus, either physical or chemical, which is con- 
veyed to the muscle through a nerve that is very sensi- 
tive and able to convey stimuli quickly and easily. 

The variety of movements that we are capable of mak- 
ing is due to the number, shape and arrangement of 
muscles and their relation to the bones. The bones are so 
arranged that they maintain the shape of the body and 
act as levers to aid the motion. 

Neither nerves nor bones can initiate a motion. The 
muscles are responsible. 

Muscular activity is important because it is inti- 
mately connected with every function of the body. Dur- 
ing activity, disintegration of complex substances in the 



120 PHYSIOLOGY 

muscle and the oxidation of resulting products, occur. 
From unstable compounds, stable compounds are 
formed. These stable compounds are no longer of use 
to the bodily machine so they are given off as wastes 
through the excretory organs. The chemical actions 
involved set free an enormous amount of heat which is 
distributed through the body, or given off from its sur- 
face. The disappearance of complex substances creates 
a demand for food and oxygen which are brought to the 
muscle through the quickening of the circulation and 
respiration, and used for the manufacture of new com- 
plex substances. 



PAKT II 



INTEODUCTION 

In the second half of this book the great groups of 
animals will be considered in order to show how the 
functions are affected by structural development. De- 
scriptive details which have already been presented 
many times fully and delightfully will be reiterated 
only in so far as may be necessary to emphasize the 
fact that the life processes in living organisms continue 
in direct response to an involuntary conformity to 
natural laws. 

Each science has its own body of well-established 
laws, yet year by year the limits of the sciences become 
more and more vague, and their laws more and more 
interdependent, until it is almost impossible to say 
where one science begins and another ends. In time to 
come, as more and more light is vouchsafed, we may 
find that all natural phenomena are governed by a 
single ultimate comprehensive law, of which the actions 
of the human body and mind are but a very high 
expression. The gaps left unexplained by the law of 
evolution will be bridged and it will then no longer 
be a mystery how matter first originated, became en- 
dowed with life, and reached up to intelligence and to 
conscience. Human thought has not yet conquered 
these four problems, but the gradual advance and mar- 
velous unity in the processes that we understand teach 
us that a leap in the scheme of nature is incredible. 

123 



124 PHYSIOLOGY 

The infinite variety that exists in nature is mar- 
velous, but the infinite unity is much more marvelous. 
A multitude of animals and plants, each with its own 
peculiarities, exists, but the same life processes depend- 
ent upon the same simple principles, are found in them 
all. And the manner in which these are manifested is 
the whole of physiology. It has been customary to 
emphasize the differences that exist between organisms, 
but emphasis should rather be laid upon their similarity. 

All organisms are composed of protoplasm, or living 
matter. What this protoplasm is we know only in part. 
We can analyze it chemically after killing it and thus 
find what elements are present in dead protoplasm. 
But what the subtle thing is which distinguishes this 
dead protoplasm from living protoplasm we do not 
know. Living protoplasm has the power to move, to 
grow, and to reproduce ; and in this respect the pro- 
toplasm of the simplest animals and plants in no wise 
differs from the protoplasm of the highest animals and 
plants. The essential processes of physiology go on 
in the ameba as perfectly as in human beings, although 
the ameba is but a single cell not even possessing a 
definite cell wall. It can move from place to place; 
it can take in food and oxygen, carry these to any and 
all parts of its body and out of them make new 
protoplasm; it can give off waste materials, and it can 
produce its own kind. Physiologically human beings 
can do no more. 

All living things may be divided into two classes, 
animals and plants. It seems easy to distinguish these 
from each other, for the higher forms that we meet 



INTRODUCTION 125 

daily have developed definite and very different char- 
acteristics; bul ii is noi easy to formulate a distinction 

thai applies equally to the lower forms, for in the lowest 
animals and the lowest plants the living mailer is so 
slightly differentiated, that in both its physiological quali- 
ties are manifested in the same way. They move readily 
from place to place, they make new protoplasm out of 
the non-living matter which they assimilate, and they 
reproduce their kind after the same methods. The only 
distinction which holds universally for both lower and 
higher forms concerns assimilation. Animals must have 
solid food. Plants can take in only liquids and gases, 
but out of these they manufacture within their bodies 
the complex solids that they too need. 

Organisms may be again divided into two classes, 
those which are composed of a single cell and those 
which are composed of many cells. In one-celled 
forms there is no distinction between the cells of any 
particular species, they are all alike. Within the cell 
the protoplasm moves, assimilates food and manufac- 
tures new protoplasm ; and the organism as a whole 
moves, assimilates food and reproduces new organisms. 
Thus the characteristics of living matter characterize 
the cell as an independent organism. 

In many-celled organisms the cells differ from each 
other in appearance and work. The protoplasm in 
each cell has the qualities of living matter; it moves, 
assimilates food, and reproduces itself; but the cells are 
not independent organisms. They are associated with 
each other in groups called tissues and organs, and each 
group does its work toward maintaining the life of the 



126 PHYSIOLOGY 

organism. The sum of these activities represents the 
activity of the independent organism, the particular 
way in which the many-celled organism as a whole 
shows its living characteristics, motion, reproduction, 
assimilation. 

In different organisms the differentiation of the cells, 
tissues, and organs, has proceeded along different lines, 
or, proceeding along the same line, has reached different 
stages of development. According to the resulting pe- 
culiarities animals are divided into groups. Each 
group of organisms has its own peculiar way of moving 
from place to place, of assimilating food, and of repro- 
ducing its kind. These characteristics can not differ 
essentially in the various groups, for an organism can 
not assume characteristics other than those of the living 
matter which composes its cells ; but they may differ in 
details, and these details depend on the peculiar ar- 
rangement of the cells of its body into tissues and 
organs, and the extent of their differentiation. 

Some organisms have developed special organs for 
locomotion whose activity is governed by mechanical 
principles. To know how an animal moves from place 
to place, then, we must know how the organs of locomo- 
tion are constructed. Some animals have special means 
of protecting their young until they can fend for them- 
selves. The more highly developed the animal, the 
longer is its period of infancy and the more perfect the 
arrangements for protection. We must know, then, 
something about the special organs set apart for repro- 
duction and something about the habits of the group. 
As animals increase in complexity, the digestive appa- 



INTRODUCTION 127 

ratus becomes more complete in its details and special 
arrangements for breathing are developed. We must 
know the structure and location of these organs in dif- 
ferent groups in order to understand the conditions 
under which they do their work. We must know what 
the animal eats, how it eats, how the food is digested, 
absorbed, converted into protoplasm, and how the wastes 
are given off. These things happen in all animals and 
are governed by the same principles. 

To study any particular animal, then, we study the 
peculiarities of structure which control its method 
of moving, its method of assimilation, and its method 
of reproduction. 



CHAPTEE VII 
PROTOZOA 

Habitat. — Protozoa, or one-celled animals, exist in 
great numbers. They vary greatly in shape, appear- 
ance and habits. They are found in stagnant water, 
in fresh water, in the sea, in moist earth, and as para- 
sites in the bodies of other animals. Malaria is due 
to one of these forms which becomes parasitic in the 
bodies of human beings. The common forms may be 
obtained for study by filling shallow glass dishes with 
water plants, covering them with water and allowing 
them to decay. Within two weeks if the water is ex- 
amined from time to time many different forms will be 
found. 

The Ameba. — The simplest of these animals is the 
ameba. It has not even a cell wall. It is nothing but an 
undifferentiated mass of granular protoplasm contain- 
ing a nucleus. It moves from place to place, grows, and 
reproduces, but in the most primitive way. Food is 
taken in at any point, indigestible materials pass out at 
any point, and any part of the cell is used for loco- 
motion. (Figs. 4, 16.) 

The irritability of the protoplasm is responsible for 
locomotion. The protoplasm flows within the cell and as 
there is no confining wall the position and shape of the 

128 



PROTOZOA 129 

cell depend upon the direction and the amount of the 

flow, [f the protoplasm touches food it flows around 
the particle, engulfs it, and after the nourishing part 
has been assimilated, flows away, leaving the residue 
behind. The animal thus moves from place to place and 
eats by means of projections of flowing protoplasm that 
appear and disappear at any point of the constantly 
changing outline. The ameba does not differ from 
other members of the group in its method ol assimila- 
tion and reproduction. 

More Highly Specialized Forms. — Other one-celled 
forms are more highly developed. A delicate wall sur- 
rounds the protoplasm, making the outline of the cell 
definite. Different regions are specialized for the per- 
formance of special work. The surface is more or less 
covered with fine, hair-like appendages called cilia 
which by their movement propel the animal from place 
to place as oars propel a boat (Fig. 72). At a definite 
point is an opening comparable to a mouth, surrounded 
by a circlet of cilia. This opening leads through a short 
passageway, comparable to a gullet, into the protoplasm. 

The food consists of the bodies of smaller organisms. 
They are caught in the whirlpool formed by the move- 
ment of the cilia about the mouth and are drawn 
through the gullet into the body, where they may be 
seen with the aid of a compound microscope (Fig. 73). 

Food Substances. — The protoplasm of these organ- 
isms contains the food substances which all animals 
require — water, salts, carbohydrates, fats and proteids. 
Surrounded by a drop of fluid these are carried about 
in the stream of circulating protoplasm until they are 



130 



PHYSIOLOGY 




A B 

Fig. 72.— Paramecium. A, from the left side, anterior end directed upwards ; B 7 
from the ventral side, anterior end directed upwards ; an, anal spot ; c.v., con- 
tractile vacuoles; f.v., food-vacuoles ; w. v., water vacuoles; m, mouth; mac, 
mic, nucleus; ce, oesophagus; #, vestibule. The arrows inside indicate the direc- 
tion of the protoplasmic currents, those outside the direction of water currents 
caused by the cilia. (From Sedgwick and Wilson.) 

digested. The nutritive portion is thus brought to every 
part of the body where it may be used for the manu- 
facture of new protoplasm, and the indigestible refuse 
to a weak spot in the body wall through which it is 
ejected. 



PROTOZOA 



131 



Wastes. — The constant activity of these animals in- 
volves constant disintegration of protoplasm, and now 
protoplasm to take its place must be constantly made 
from the food substances. This involves a series of 



ill 



r\ 










Fig. 73.— Ameba after a full meal, consisting of a large diatom (dt) ; n, nucleus \f.v. 
food vacuoles ; c.v., contractile vacuoles. (From Sedgwick and Wilson, after 
Leidy.) 



chemical actions. Complex unstable substances disin- 
tegrate and new unstable substances are built up and in 
the process stable substances are formed. These stable 
substances can no longer be used by the body either for 
the manufacture of protoplasm or for the production of 
heat. They are therefore given off as w 7 astes. The 
principal wastes are carbon dioxide and water vapor 



132 PHYSIOLOGY 

which are given off by osmosis ; and urea which is given 
off in solution by the contractile vacuole. 

This organ is a true excretory organ, comparable to 
the kidney of the higher forms. It is a clear space 
which appears and disappears rhythmically, enlarging as 
it becomes filled with fluid and contracting to eject 
the fluid from the body. This organ must not be con- 
fused with the anal spot. The excretory organ gives 
off waste from the protoplasm itself, but from the anus 
pass off those parts of the food which can not be made 
into protoplasm and which therefore have never been 
a part of the body of the animal. 

Respiration. — In one-celled animals the entire body 
wall is surrounded by water which contains oxygen in 
solution. By the process of osmosis oxygen passes into 
the body at any point and carbon dioxide passes out. 
This occurs not because the animal needs oxygen, but 
because a gas passes in the direction of the least pres- 
sure. The animal has no choice in the matter. 

Reproduction. — Two methods of reproduction exist. 
The simplest of these is fission, a purely non-sexual 
process by which an animal splits into two parts each 
of which becomes a new animal. This process can not 
continue indefinitely. It is supplemented by a sexual 
process called conjugation. Two animals come close 
together and exchange either the whole or a part of the 
nucleus and separate. This brings about a rejuvenation 
by which both animals regain the power of fission. 
They are then able to divide and again divide until 
enough cells are formed to make a well-differentiated 
animal were they but joined together. As a rule con- 



PROTOZOA 



133 



(ligation takes place between two similar individuals, 
but in Vorticella and a few allied forms ii is modi- 
fied in such a way thai it directly foreshadows the 
fertilization of higher forms. A hud is given off from 



C^ 



r- '■'• - 







Fig. 74.— One of the vorticellidae (Epistylis) in budlike conjugation, r, buds 
arising by division; I; a bud conjugating. CFrom Her twig, after Grecff.) 



the side of an individual, which divides into eight tiny 
motile cells. Each of these attaches itself to a full- 
sized individual and is completely absorbed by it (Fig. 
74). The resulting cell regains the power of rapid cell 
division. 

Summary. — Protozoa are microscopic, one-celled ani- 
mals in which one cell performs all the functions. The 
cells of any particular species are not differentiated 
from each other, but within the cell special cell-organs 
may develop. Protozoa are able to move from place 
to place by means of flowing protoplasm or by means, 



134 PHYSIOLOGY 

of cilia. They assimilate the bodies of other organisms 
which contain all the necessary food substances ; give 
off nitrogenous wastes through a special excretory 
organ; breathe through the entire surface of the body; 
and reproduce non-sexually by fission and sexually by 
conjugation. 



CHAPTER VIII 
CCELENTEKATA 

Many-Celled Animals. — Many-celled animals prob- 
ably owe their existence to some accident which pre- 
vented complete fission. The cells after division re- 
mained attached. Those that w r ere subjected to different 
environment assumed different functions, and became 
different in structure. Those which developed a similar 
structure with power to do the same kind of work became 
banded together in groups called tissues or organs. 

Many-celled animals have in this way developed cer- 
tain characteristics in common. The cells of which they 
are composed have been subjected to the same kind of 
influences and have undergone development in the same 
general directions. In all many-celled animals, there- 
fore, the same tissues are present. When these tissues 
are once established their development becomes one of 
degree, not of kind, and the quality of the work that 
they are able to accomplish becomes dependent merely 
on the degree of development. 

The Primary Layers. — The cells were first arranged 
in two layers. The outside layer, or ectoderm, formed 
the skin and was protective in nature ; the inside layer, 
or entoderm, formed the lining of the digestive tract and 

135 



136 



PHYSIOLOGY 



assumed the functions of digestion and absorption of 
food substances. For some time probably animals re- 
mained in this primitive stage; there is still in exist- 
ence a large group which has never passed beyond it. 
Later a third layer, the mesoderm, developed between 
the ectoderm and the entoderm, and the three primary 
layers were established. All higher animals pass 
through the layer stage in their development. From 
these layers are developed their highly organized tis- 
sues ; from the ectoderm the . protective organs, — skin 
and its appendages, nerves and sense organs; from the 

entoderm everything which 
has to do with alimenta- 
tion, — digestive tract, di- 
gestive glands, lungs ; 
from the mesoderm, every- 
thing else, — bone, muscles, 
blood, connective tissue, 
many glands. 

Tissues of the Ccelen- 
terata. — In the coelente- 
rata all the functions of the 
body are performed by the 
tw T o primary layers (Fig. 
75). The third layer is 
rudimentary. This group 
of animals is particularly 
interesting because it is 
transitional. Within it 
most of the tissues found in higher organisms are es- 
tablished. We have the beginning of muscle tissue, 




en s ek 

Fig. 75.— Section of wall of hydra, en, 
nettle cells ; ek, ectoderm ; s, sup- 
porting layer ; en, entoderm. (From 
Hertwig, after Schulze.) 



((KLKXTERATA 



137 



nerve tissue, sense organs, the skeleton, a definite ali- 
mentary canal, and definite reproductive organs. 

Distinguishing Characteristics. — The name coelen- 
terata comes from two Greek words that mean hollow 
intestine. It was given to the group because of the 
prominent digestive cavity which occupies the whole of 




Fig. 76.— Hydra showing tentacles and the enlargements which give rise to the 
sperm and egg cells. (From Hertwig.) 

the interior of the body, to the exclusion of the separate 
and distinct body cavity which exists in most of the 
higher forms. This common characteristic marks the 
relationship between such apparently diverse forms as 
the hydra, tnl jellyfish, and the sea anemone (Figs. 76, 
77, 78). In the hydra there are only two layers of cells 
and these are arranged in a double, bell-shaped wall so 



138 



PHYSIOLOGY 



that a central spacj is formed with one opening to the 
outside. 

The jellyfish is closely related to the hydroid (a salt- 
water form very similar to the fresh-water hydra) but 




Fig. 77.— Jellyfish. (From Hertwig, after Haeckel.) 

the resemblance has been obscured, for the depressions 
and elevations on the surface of the. hydroid have been 
intensified in the jellyfish, and through the separa- 
tion of the two layers in the wall by a structureless jelly 



CCELENTERATA 



139 



the central cavity has assumed a definite tubular shape 
(Figs. 79, A; 7t), B). 

In the 1 sea anemone the middle layer, or mesoderm, 
is more highly developed than it is in the jellyfish, and 




Yiq, 78.— Diagram of sea anemone. (From Kingsley, after Emerton.) 



it does not have the jelly-like character. The central 
cavity is more like that of the hydra except that the 
elevated hypostome is pushed in and hangs down as an 
oesophagus inside the animal. It is held in place by 
partitions having long attached filaments that assist in 
the digestion of the food (Fig. 79, C). 

Assimilation. — In this group the first step in the de- 
velopment of the digestive system is taken. The tract 
may be described as a blind tube with a single opening 



140 



PHYSIOLOGY 



to the outside through which food enters and waste is 
ejected. 

Guarding this opening is a circlet of tentacles, highly 
developed, contractile organs. In the tentacles are de- 




Fig. 79.— Diagram of sections of A, hydroid ; J5, jellyfish ; C, sea anemone. (After 
Hertwig.) 

veloped nettle cells, each of which has a little tube 
coiled in it which can be thrown out when the cell is 
stimulated. The tubes set free an irritating poison 
which paralyzes smaller animals and serves not only as 
a means of defense but aids in the capture of food. 



OOELENTERATA 141 

Through the contraction of the tentacles the food is 
forced into the cavity. Partial digestion takes place 
there. Non-nutritive substances pass off through the 
opening; the nutritive portions are engulfed by the 
entodermal cells, which have the power of sending out 
ameboid branches. Complete digestion follows in the 
entodermal cells, and the products pass from cell to 
cell by osmosis. (Fig. 75.) 

As the digestive tract extends to all parts of the body 
food is distributed without the intervention of a special 
circulatory apparatus. It therefore performs the office 
usually performed by blood vessels. 

Breathing takes place through the outer cell walls. 
Oxygen dissolved in the water passes by osmosis into the 
cells and carbon dioxide formed in the cells passes into 
the surrounding water. 

Irritability. — In addition to the ameboid motion of 
the entodermal cells and the spring-like motion of the 
nettle cells, the cells of both ectoderm and entoderm 
send out contractile branches which foreshadow 7 the 
muscle cells in higher forms. The simultaneous con- 
traction of these branches forces the animal to contract 
as a whole or allows a curious form of locomotion from 
place to place. 

Some forms move about freely, some are fixed firmly, 
and some are able to hold fast to a support by suction. 
The jellyfish moves by the rhythmical contraction of 
its swimming bell. The bell relaxes and the hollow 
becomes filled with water, it contracts and the water is 
forced out. As this occurs rhythmically the animal 
moves jerkily through the water. The sea anemone at- 



142 



PHYSIOLOGY 



taches itself by flattening its surface against a rock until 
the air is forced from beneath. The pressure of the air 





Fig. 80.-^4, Coral showing living animai. (From Hertwig, after Heider.) B, Coral 
skeleton. (From Hertwig, after Klunzinger.) C, Diagrammatic section of coral 
showing flesh; above the line, ab, the section passes through the oesophagus, s ; 
below the line it is lower down; the coral skeleton is black. (From Hertwig.) 



above then holds it to the rock. By muscular contrac- 
tion it is able to creep slowly along. 

Fixed Forms. — Hydroids and corals are firmly at- 



CCELENTEEATA 14:; 

tached, usually by the formation of a supporting skele- 
ton. In many hydroids a hard wall is formed on the 
outside of the animal, but in corals it is internal as 
well (Fig. 80). These animals can not move from 
place to place, but they can contract the soft part of the 
body. Corals are like sea anemones in structure except 
for the skeleton formed in corals by the deposit of 
calcareous salts in the mesoderm. 

Nervous System. — Most of the fixed forms have no 
nervous system ; the surface of the body is, however, ex- 
tremely sensitive to contact. The motile forms have a 
definite nervous system composed of a central nerve 
ring from which branches are given off. Some of 
them have also simple sense organs which are sensitive 
to light and sound vibrations. 

Colonial Forms. — Many forms develop buds which 
do not become detached ; these grow into distinct in- 
dividuals, which live together in a colony. Frequently 
members of a group formed in this way become adapted 
to the performance of special work, and the colony 
comes to resemble a more highly-differentiated, many- 
celled animal. It becomes a question then whether the 
whole colony is to be regarded as a collection of sepa- 
rate individuals which live together for the common 
good, or as a single animal with exceedingly well-de- 
veloped parts (Fig. 81). 

Reproduction. — In all of these forms reproduction 
is either non-sexual (by budding, a process allied to 
fission) or sexual (by the union of dissimilar cells). 
In budding a mass of cells grows out with the power to 
develop into a new individual which may, or may not, 



144 



PHYSIOLOGY 



be cut off from the parent. The sexual process does 
not differ in essence from the conjugation of the one- 
celled animal, but it is necessarily modified by the 
fact that in a many-celled animal as the cells are 




Fig. 81.— Portion of a colony, gp, reproductive polyp; mp, defensive polyp; 
tp y nutritive polyp. (From McMurrich, after Hincks.) 



differentiated not all of them can enter into the process. 
Special cells are therefore manufactured by special 
organs and set apart for reproduction. In one animal 
they are large, round, quiescent ; and in another they 
are small, irregular, motile. These cells ase set free 
in the water. They meet as the one-celled animals do 



CCELENTERATA 14H 

and unite, forming new cells with the power of eel] 
division and cell differentiation ( Figs. 54 ; 55, A). 

Alternation of Generations. — In addition to the form 
relationship there is a very curious parental-relationship 




Fig. 82.— Hydroid showing alternation of generations, h, polyps which have given 
off medusa buds ; mk, medusa buds; m, separated medusa. (From Hertwig, 
after Lang.) 

between the hydroid and the jellyfish. The hydroid is 
colonial. The individuals increase in number on the 
common stalk by continual budding. Some of these 
buds break off and become free-swimming jellyfish 
which assume a sexual character. They produce eggs 
and sperm which unite, divide, and differentiate to form 



146 PHYSIOLOGY 

a hydroid. This hydroid forms a colony which in 
course of time gives rise to jellyfish, and so the process 
repeats itself (Fig. 82). This process is called alterna- 
tion of generations. 

Summary. — The coelenterata are symmetrical ani- 
mals characterized by the absence of a distinct body 
cavity, by the presence of a blind digestive tract, and 
by the presence of only two layers in the body wall. 
The third layer sometimes present is rudimentary and 
may be jelly-like. 

Movement of the organism as a whole is produced 
by the activity of contractile tissue similar to the mus- 
cles of higher forms. In fixed forms this results in a 
change of form and position; in free forms, of move- 
ment from place to place. An especially irritable cell, 
called the nettle cell, throws out a tube which contains 
poison. This protects the animal from its enemies and 
aids it in capturing food. 

Assimilation takes place in a tube with but one open- 
ing to the outside. The oesophagus may project outward 
as in the hydra, or it may be turned inward and be 
held in place by septa as in the sea anemone. 

Reproduction is both sexual and non-sexual, and in 
some species the sexual and non-sexual forms may alter- 
nate in succeeding generations. 

In some forms a skeleton is present made by the 
deposit of calcareous salts in the tissues. 



CHAPTER IX 
ECHINODEKMATA 

Characteristics. — The echinodermata are a sharply- 
defined, well-established group. The name refers to the 
spiny skin, and this together with a symmetrical, radiate 
structure characterizes all the members of the group. 
They were once classed with the coelenterata, but the 
groups differ materially. 

The most important characteristics are the presence 
of a body cavity quite distinct from the digestive tract, 
the presence of a circulatory system, and the develop- 
ment of the complete alimentary canal with an open- 
ing at both ends. Further, the tissues are much more 
highly differentiated than those of the coelenterata. 
There is a well-defined external skeleton made of hard, 
movable plates comparable to the bones of higher ani- 
mals, a muscular system that controls complex move- 
ments, gills which are responsible for respiration, a 
blood circulation confined to definite vessels, a repro- 
ductive and a nervous system. 

As animals increase in complexity more and more 
attention must be paid to their structure because the 
arrangement of associated cells which determines the 
peculiar form of the animal, determines also the pecu- 
liar way in which the physiological characteristics of the 

147 



148 



PHYSIOLOGY 



animal, irritability, assimilation, and reproduction, 
manifest themselves. 

The Starfish. — Perhaps the best-known echinoderm 
is the starfish. It has a symmetrical, flattened, star- 




Fig. 83 A.— Starfish, dorsal surface. (From McMurrich.) 

shaped body (Fig. 83 A) with, as a rule, five rays, 
though there may be as many as twenty. It is covered 
with a protective skeleton made of movable plates which 
allow the rays to bend easily in any direction. A 
mouth is in the center of the ventral side (Fig. 83 B). 
On this side, in each arm, is a groove in which are 
situated the locomotor organs, commonly called tube 
feet. These tubes are connected with a system which is 
a peculiar characteristic of the echinoderms. 

Symmetry. — The similarity of the rays of the star- 



ECIIINODERMATA 149 

fish has given rise to the phrase radial symmetry. Sym- 
metry involves a repetition of similar parts. Externally 
the arms of the starfish radiate from a common center 




Fig. 83 B.— Starfish, ventral surface (placed on back, righting itself). (Prom 
Packard, after Romanes.) 

and except for the perforated plate on the dorsal sur- 
face the five parts of the body duplicate each other. 
Internally the organs are correspondingly repeated. 
The perforated plate gives the body a rudimentary 
two-sided or bilateral symmetry, for a line drawn 
through this plate to the tip of the opposite ray divides 
the animal into two similar halves. 

Internal Structure.— The alimentary system is a tube 
open at both ends that passes through the animal dorso- 




150 PHYSIOLOGY 

ventrally (Fig. 84). It has two enlargements which 
somewhat obscure its tube-like character, each of which 
is made of five pouches, one for each ray. The pouches 
of the thin-walled stomach on the dorsal side are further 
subdivided, and are continued to 
form the ducts of the hepatic 
glands, or livers, found in each 
ray. The other organs are also 
arranged with reference to the di- 
^<l( \\ gestive tract. The nervous, circu- 

' latory and water-vascular systems 

Fig. 84.— Dorsal view of the J 

alimentary canal of a take the form of rings which sur- 

Btarfish. Diagrammatic. ^^ ^ ^^g^ and give off 

an arm for each ray. At the end of each radial nerve is 
a sense organ called an eye-spot that is sensitive to light. 

Irritability. — Irritability manifests itself in change 
of form and position and in movement from place to 
place through the activity of muscles whose cells are 
specially modified for contraction. These are aided by 
nerves whose special form of irritability consists in their 
power of carrying stimuli quickly. They thus increase 
the rapidity of movement. 

Mechanics of Locomotion. — In moving from place to 
place, a starfish contracts the muscles which bend a ray. 
The ray moves in a definite direction and then holds 
fast by means of its tube feet until the body of the ani- 
mal is adjusted to the new position. The tube feet 
stiffen, and force the air from beneath them. They are 
then held fast to the damp surface by the weight of the 
surrounding air. The pressure exerted on them by the 
air may be found approximately by comparing the ap- 



ECIIINODEPvMATA 



151 



proximate area of the bottom of all the little tube leei 
involved with a square inch and multiplying the re- 
sult by fifteen, for every square inch of surface bears 
the weight of fifteen pounds of air. 

The lube feet are able to stiffen because of their con- 
nection with a system of tubes in the animal. Sur- 
rounding the oesophagus is 
a tubular ring which gives 
off a blind tube in every 
ray and in addition a tube 
with calcareous walls that 
opens to the outside on the 
dorsal side in a perforated 
plate. Each radial canal 
gives off at regular in- 
tervals pairs of canals 
which connect with the 
tube feet. These are hol- 
low muscular tubes each 
of which ends inside the 
ray in a little sac and out- 
side the ray in a sucker 
(Fig. 85). The system is filled with fluid 
sacs contract fluid is forced into the feet and they 
stiffen, if the feet contract the fluid is forced back into 
the sac and the feet are withdrawn. 

Assimilation. — Assimilation takes place through the 
respiratory system and the alimentary canal. Special 
organs for the absorption of oxygen are developed on 
the dorsal surface in the form of gill-like outgrowths. 
Water passes over them and the oxygen it contains 




Fig. 85. — Water-vascular system of 
starfish, a, ampullae or sacs ; ab, tube 
feet ; c, radial canal ; m, perforated 
plate ; n, radial nerve ; r, ring canal ; 
5, stone canal. (From Hertwig.) 



If the 



152 PHYSIOLOGY 

enters the body through their thin walls and carbon 
dioxide passes off. 

The starfish eats oysters and similar animals which 
contain the five food substances which it requires. It 
wraps itself around the oyster, attaching itself firmly 
to the shell by means of the tube feet. It then pulls 
until the oyster becomes so fatigued that it can not 
hold its shell shut any longer. As soon as the shell 
opens the starfish pushes its stomach out through its 
mouth, surrounds the flesh of the oyster, and with the 
aid of the juices secreted by the livers, digests it. When 
it has finished the stomach is drawn back into the ani- 
mal by the retractor muscles and the undigested material 
is left behind. Through this method of feeding some 
starfish have so degenerated that the alimentary canal 
has lost its dorsal opening. 

Reproduction. — Reproduction is sexual. The organs 
which form the sexual products lie at the junction of 
the rays and open to the outside through ducts. They 
are paired and during the breeding season extend well 
into adjoining rays. As in coelenterata, eggs and sperm 
are formed in separate animals. They are turned 
loose in the water, where they meet and unite, forming 
a new cell with the power of cell division and differ- 
entiation. The young are free-swimming and, as they 
differ greatly from the adult, they are called larvae. 
They are bilaterally symmetrical but show not a trace of 
radial symmetry. 

Regeneration. — The only form of non-sexual repro- 
duction that seems to be present is commonly called 
regeneration. It is present to a remarkable degree in the 



ECHINODERMATA 153 

echinoderms. If a ray is injured the animal throws 

off the whole ray and then makes another to take its 
place. In some species a single ray with perhaps a 
small portion of the central disk attached is able to 
form an entire animal. 

Summary. — The echinoderms are marine forms with 
calcareous skin. They show marked radial symmetry as 
well as a rudimentary bilateral symmetry. They have 
a well-developed alimentary canal with two openings to 
the exterior. They breathe through thin-walled out- 
growths on the dorsal surface. A w^ell-developed cir- 
culatory system carries food and oxygen to all parts 
of the body. Locomotion is effected through the water- 
vascular system with the aid of muscles and nerves. 
Reproduction takes place sexually; a free-swimming 
larva is formed which in order to reach the adult form 
must undergo a metamorphosis. The power of regen- 
eration is marked. 



CHAPTEE X 
MOLLUSCA 

Shells. — Shells in infinite variety may be picked up 
on the seashore. These appear in such numbers and 
have such well-marked characteristics that the study 
of them is a science in itself. However, in the interest 
that attaches to collecting and classifying them it should 
not be forgotten that these shells are merely external 
skeletons formed for the protection of living animals. 

The Living Animal. — The animal which forms the 
shell is more important than the shell, and the manifesta- 
tion of its activities the essential thing. The name mol- 
lusca is a recognition of this. It comes from the Latin 
word mollis (soft) and refers to the soft body within 
the shell. The shell is so wonderfully adapted to the 
body within that variations in the one are repeated in 
the other. Characteristics of the living animal may 
often, therefore, be determined merely from a study of 
the shells. 

Formation of the Shell. — The shell is formed through 
the activity of a flap of skin called the mantle which 
covers the body of the animal. The outer surface of the 
mantle secretes carbonate of lime, out of which the shell 
is formed. The shell may split down the middle line 
forming two pieces, or valves, united by a hinge. It 

154 



MOLLUSOA 



155 




Fig. 86.— Chiton . (From 
KiDgsley, after Haller.) 



may split transversely into eight valves, or it may re- 
main in one piece (Fig. 86). If it remains in one 
piece it may remain flat, or it may 
become tubular or coiled in a spiral 
(Fig. 87). As the mantle is con- 
tinually active, and the animal 
constantly growing larger, the new 
layer of shell always extends a lit- 
tle beyond the old layer. The 
oldest part of the shell is thus 
always the thickest and each new 
layer is indicated by a line of 
growth. The shell is a very per- 
fect reproduction of the mantle. 
Even colored spots and outgrowths from its surface 
reappear on the surface of the shell. 

The Clam. — In a common mollusc like the clam (Fig. 
88) the body is sac-like and is bilaterally symmetrical. 
It is divided into two parts: an upper or dorsal part 
which contains the internal organs (Fig. 89), and a 
lower, muscular part called the foot which controls loco- 
motion. The mantle is attached to the dorsal, or upper, 
edge of the body and hangs down on each side of the 
body. Its edges may be entirely separated, or they may 
be united in such a way that three openings are formed. 
Through the largest of these the large muscular foot 
passes ; through the other two, currents of water. The 
two smaller openings, called siphons, are guarded by a 
circlet of cilia whose motion causes a current. Through 
one water enters carrying food and oxygen ; through the 
other comes out water carrying waste. These siphons 



156 



PHYSIOLOGY 



may be developed to such an extent that an animal may 
bury itself deeply in mud or in piles and yet get the 
necessary food and oxygen (Fig. 90). 






Fig. 87. -Various forms of shells. (From Hertwig.) 

Gills. — In the space between the mantle and the body 
extend on each side two other folds of skin called 
gills. They are very thin and are permeated with thin- 
walled blood vessels by means of which blood is brought 
into connection with oxygen dissolved in the water. 



MOLLUSCA 157 

In land molluscs gills are absent, bul the walls of the 
mantle chamber are moist and lined with fine blood 
vessels. They act like lungs. As air circulates freely 




Fig. 88.— Clam with foot and siphons extended. (From Kingsley.) 

through the mantle chamber, oxygen can pass into the 
blood and carbon dioxide from the blood into the air. 

Circulatory System. — The body cavity is very small. 
It is practically reduced to the small chamber in which 
the heart is situated. The heart is divided into a ventri- 
cle which sends the blood over the body and an auricle 
which receives the blood from the gills. The system 
is not closed, the vessels open into large spaces or 
sinuses. In the squid an extra set of contractile organs 
called branchial hearts situated at the base of the gills 
force the blood to pass through the gills. 

Alimentary Canal. — The alimentary canal is a well- 
developed tube. On its way through the body it passes 



158 



PHYSIOLOGY 




MOLUCCA 



L59 



directly through the heart. In some forms it is so bent 
on itself thai it ends close to the month. A well-devel- 
oped liver and very large sexual organs fill the remaining 
space. 

Nervous System. — The nervous system consists of 
three pairs of ganglia con- 
nected by cords. These are 

associated with three sets of 
organs, sensitive to 
or sound vibrations, 
eves vary from mere 



sense 
light 
The 



spots sensitive to light which 
may be situated on the man- 
tle, the siphon, the tips of the 
tentacles, or the back, to the 
well-developed eyes of the 
squid which are situated on 
the side of the head and are 
almost as well developed as 
the human eye. 

Economic Value. — Mol- 
luscs have great economic 
value. Clams, oysters and 
scallops are highly prized for 
food. The precious pearl is 
formed by the oyster. The 
oyster and the abalone furnish 
the mother of pearl used ex- 
tensively in the manufacture 
of such articles as buttons 
and knife handles. The ink that is found in squids 
is used in the manufacture of sepia. It is useful to 




Fig. 90.— Long clam buried in the 
mud. (From Kingsley.) 



160 PHYSIOLOGY 

the animals, for it obscures them from their enemies 
when it is poured into the water. Many molluscs 
do an enormous amount of damage by boring with a 
file-like organ called the lingual ribbon into boats 
and piles. Some of the larger forms like the squid 
have been known to swamp boats and cause the loss 
of life. 

Characteristics of the Group. — Like other animals 
molluscs are made of living cells which are grouped in 
well-defined tissues. They are irritable, they assimilate 
food and oxygen, and they reproduce their kind. 
Through the activity of the muscular and nervous sys- 
tems they are able to move from place to place, and to 
open and close the shell. Digestion is accomplished in 
the alimentary canal with the help of the juices secreted 
by the liver. The canal is a tube with a single enlarge- 
ment called the stomach. It is open to the outside at 
both ends. As it is too long to pass directly through the 
body it is twisted on itself. The great length of the 
tube ensures a large digestive surface. 

Oxygen enters the body at a definite point through a 
specially adapted membrane found on the surface of the 
gills. Water carrying oxygen in solution passes over its 
surface. By osmosis oxygen enters and carbon dioxide 
passes off. 

Oxygen and digested food products are carried to 
every part of the body by means of a well-developed cir- 
culatory system. 

Wastes are given off through the activity of kidney- 
like organs called nephridia which take the form of con- 
voluted tubes open at both ends. One end opens to the 



MOLLUSCA 



161 



outside, the other into the pericardium, a reduced body 
cavity in which the heart is situated. 

Reproduction is sexual, that is it takes place through 
the union of two dissimilar cells, the egg cell and the 
sperm cell. Both eggs and sperm may be found in the 
same individual (land snail), but the sexes are usually 
separate. After fertilization a larval form is developed 
which through a series of changes called a metamor- 
phosis becomes like the parent form. 

The group of mollusca is divided into five classes: 
eight-valved forms in which the nervous system is much 
simplified; very primitive one- 
valved forms in which the shell 
is tubular; bilaterally sym- 
metrical, two-valved forms with 
paired organs, without head or 
appendages ; one-valved forms 
with coiled shell which have a 
head, bearing eyes and tentacles, 
a creeping foot, and unpaired 
organs, no gills, the walls of the 
mantle cavity acting as lungs ; 
and more highly developed 
forms having a single shell or 
none, unpaired mantle and 
mantle cavity, one or two pairs 
of gills, one or two auricles, one or two pairs of branchial 
hearts, an ink sac, and a well-developed head bearing 
eyes and tentacles (Fig. 91). By rhythmically forcing 
water out of the siphons they are able to swim. To this 
group belong the squid and the devil fish. 




Fig. 91.— The squid (ventral view). 
(From Hertwig, after Hoyle.) 



OHAPTEE XI 
VEEMES 

Irritability of the Earthworm.— The most widely 
known representative of this group is the common earth- 
worm. Every one is familiar with its elongated, symme- 
trical, curiously-ringed surface. It is extremely irri- 
table and when stimulated it moves readily and quickly. 
It has no definite sense organs, but a tactile sense is 
widely distributed over the surface of its body and it is 
so sensitive that it responds even to sound vibrations. 

Mechanics of Locomotion. — Movement from place to 
place is controlled mechanically by a definite arrange- 
ment of muscles. The worm lifts its anterior end 
and stretches, thereby becoming long and narrow. It 
puts down this end and holds fast. It then lifts the pos- 
terior end and by becoming short and thick draws it for- 
ward. This end then holds fast and the anterior end 
again stretches. Through repetition of this process the 
animal progresses. Two sets of antagonistic muscles 
control this alternate elongation and contraction. They 
are arranged so that one set runs lengthwise through the 
body while the other set encircles it. As one set con- 
tracts the other set relaxes. When the longitudinal mus- 
cles contract and the circular muscles relax, the worm 
becomes short and thick ; when the circular muscles con- 

162 



VERMES 



163 




Fig. 92. — Diagram to illustrate the 
action of the setae, m, muscles ; s % 
seta; w y body wall. Dotted lines rep- 
resent the position of the seta and 
its muscles when bent in the opposite 
direction. (From Sedgwick and Wil- 
son.) 



tract and the longitudinal muscles relax, the worm be- 
comes long and thin. It holds fast by means of stiff 
hairs called sctce (Fig. 
02) which are planted in 
such a direction that the 
animal can not move 
against them. 

Surface Characteris- 
tics. — These setse may 
easily be seen with the un- 
aided eye stretching in 
two double rows the length 
of the ventral surface 
(Fig. 98). Also on this surface are little swellings 
that mark tiny openings. These are situated between 
the ninth and tenth, between the tenth and eleventh, on 
the fourteenth and on the fifteenth rings. The mouth 
is under an overhanging lip at the anterior end, and 
directly opposite in the posterior end is the anal open- 
ing. A swollen girdle encircles the middle of the body. 

One line only can be drawn on the surface that will 
divide the worm into two similar parts. It is there- 
fore bilaterally symmetrical. The repetition of similar 
rings throughout its length gives it another kind of 
symmetry called serial symmetry. As in the starfish this 
external repetition of similar parts indicates a corre- 
sponding internal repetition. 

Assimilation. — A slit down the dorsal side of the ani- 
mal and a few pins to hold the flaps of skin open will lay 
bare the interior of the animal. The alimentary canal, 
which is plainly a tube open at both ends, extends 



164 



PHYSIOLOGY 




8P 






to 


3:? 

3j 


40- 


4<? 


©. 


L^ 


£» 




Ce 


^. 




r e 


3. 




<7?3 



through the entire length of the 
animal (Fig. 94). If it is cut 
open it will be found full of 
earth. The worm burrows, and 
as it has no appendage which it 
can use for this purpose it must 
eat its way through the ground. 
The earth passes into the canal 
at the anterior end and out at 
the posterior end. During its 
passage the worm gets from the 
water and organic substances 
which the soil contains the food 
necessary for its life. The con- 
stant burrowing of worms 
loosens the soil ; further, in pass- 
ing through the intestine the soil 
becomes mixed with digestive 
juices and is ground into fine 
particles. In this way the 
earth-worm increases the fertil- 
ity of the soil and is of great 
benefit to farmers. 

The skin is a moist mem- 
brane. Through it oxygen 
passes into the blood and carbon 
dioxide out of it. 

Increase of Digestive Sur- 
face. — If the inside wall of the 



Fig. 93.— Earthworm, ventral surface, an, anus ; c, girdle ; m, mouth ; o.d., ex- 
ternal openings of the oviducts ; s, setae ; s.?\, openings of the seminal recep- 
tacles ; s.d., external openings of the sperm ducts. (From Sedgwick and 
Wilson. 



VERMES 



165 



canal is examined a fold called the typhlosole running 
its entire length will be noticed. This fold practically 
doubles the absorptive surface of the canal so that in the 
passage of food from the mouth to anus there is time 

A 




^ * ad Tt s.i n 
Fi(4. 94.-^4, diagram of a longitudinal section of the earthworm. B, diagram of a 
cross section. C, diagram showing the principal organs, al, alimentary canal ; 
an, anus; ds, dissepiments; d.v., dorsal blood vessel; s.i., ventral blood 
vessel ; c.v., circular blood vessel ; n, nephridia or excretory organs ; e.g., 
cerebral ganglia ; v.g., ventral chain of ganglia ; o.d., oviduct ; o, ovary; m, 
mouth ; cor., body cavity. (From Sedgwick and Wilson.) 

and place for the digestion and absorption of sufficient 
nourishment (Fig. 97). In the starfish where the dis- 
tance between mouth and anus is very short the same 
thing is accomplished by the large pouched-stomachs 
whose folds increase enormously the digestive surface; 
and in higher animals it is accomplished by the in- 
creased length of the canal, which in man reaches five 
or six times the length of the body. 

Circulatory System. — The circulatory system is well 
defined. The vivid red blood makes the large vessels 
which run longitudinally on the dorsal and ventral sides 
noticeable through the skin. They are connected by a 



166 



PHYSIOLOGY 



10. 



15. 



s.r 




Fig. 95.— Dorsal view of the internal organs of the earthworm, a.o., aortic arch ; 
c, crop ; e.g., cerebral ganglion ; d y dissepiment ; d.v., dorsal vessel ; g, gizzard ; 
«, oesophagus ; ph, pharynx ; s. i., intestine ; s.?\, seminal receptacles ; t, semi- 
nal vesicles. (From Sedgwick and Wilson.) 

series of circular vessels. Near the anterior end, five of 
the circular vessels called the aortic arches, become en- 



VERMES 



167 




svr 



SV?' 



Fig. 96.— Internal organs of the earthworm with alimentary and circulatory sys- 
tems removed, eg, cerebral ganglia ; ds, dissepiment ;/, funnel of nephridium ; 
np, nephridium ; o, ovary ; od, oviduct ;ph, pharynx ; r.s., seminal receptacle ; 
s.d, sperm duct ; s./, sperm funnel ; s.v .1, seminal vesicle ; t, testis, or sperm- 
ary ; v.g and v.n.c, ventral nerve cord. (From Sedgwick and Wilson.) 

larged and pulsate rhythmically (Fig. 95). They take 
the place of the heart of higher animals, and together 



168 



PHYSIOLOGY 



with the wave-like contraction of the dorsal vessel cause 
the blood to circulate. 

A Segment. — Corresponding to the external rings are 
thin partitions called septa or dissepiments that separate 
the body into little compartments called segments. Ex- 
cept for those in the anterior end that contain the re- 
productive organs and the aortic arches, the segments 




Fig. 97.— Cross section of the earthworm, a.c, cavity of the alimentary canal ; 
c, cuticle ; c.ce, ccelom ; cm., circular muscles ; c.v, circular vessel ; d.v< dorsal 
vessel ; /.m., longitudinal muscles ; n. c, ventral nerve-chain ; s, seta ; s.i.v, sub- 
intestinal vessel; s.m., muscle connecting seta of the same side; ty, typh- 
losole. (From Sedgwick and Wilson.) 

are alike (Fig. 97). Each one contains a section of the 
longitudinal muscles, a circular muscle, two pairs of 
setae, a ganglion with its pair of nerves, a circular blood 
vessel with sections of the longitudinal vessels, a section 
of the alimentary canal and a pair of nephridia, 



VERMES 169 

Excretory Organs. — The nephridia, kidney-like ex- 
cretory organs, are responsible for the elimination of 
nitrogenous waste. Each of them is a curiously twisted 
tube which opens to the body cavity through a funnel- 
shaped end and empties to the exterior through the other 
end (Fig. 96). 

The Nervous System. — The nervous system extends 
the length of the body on the ventral surface. It is a cord 
with a small swelling or ganglion in each segment, made 
of two cords only partially joined. This is particularly 
interesting because in some of the other worms the two 
cords are entirely separate and lie on opposite sides of 
the body. At the anterior end these cords separate and 
pass in a ring around the alimentary canal. The junc- 
ture on the dorsal side is marked by a double ganglion. 
The serial arrangement of the ganglia in the ventral 
cord is very important, for on it those people who trace 
the ancestry of the vertebrates to the segmented worms 
base their claim. In higher animals the spinal cord 
retains this characteristic even when the body shows no 
other trace of segmentation (Figs. 70, 71). 

Reproduction. — The arrangement by which the eggs 
and sperm come in contact with each other is extremely 
interesting. They can not be turned loose as in aquatic 
forms, for the delicate eggs and sperm would die if they 
were left unprotected on the ground. The openings 
seen near the ninth and tenth segments lead into little 
sacs called seminal receptacles situated two on each side. 
In the thirteenth segment tiny ovaries which produce 
the egg cells lie one on each side. These open to the 
outside on the fourteenth segment. Xear them are the 



170 PHYSIOLOGY 

large vesicles which surround the spermary or testis. 
These have three large lobes on each side and open to the 
outside on the fifteenth segment. 

The worm is hermaphroditic, that is, both eggs and 
sperm are present in the same animal, but self-fertiliza- 
tion is prevented by the arrangement of the organs and 
by the fact that the eggs and sperm do not mature at 
exactly the same time in each animal. Cross fertiliza- 
tion takes place in the following way. In the breeding 
season two animals come close together with the ventral 
surfaces touching, the anterior end of one directed 
toward the posterior end of the other. The ninth seg- 
ment of one thus comes in contact with the fifteenth of 
the other, bringing the opening of the male organs 
directly opposite the opening of the seminal receptacles. 
Sperm cells then pass from each worm into the seminal 
receptacles of the other. The worms then separate. 
When the eggs become ripe the ring, or clitellum, noticed 
around the middle of the worm begins to pass forward. 
When it reaches the fourteenth segment the eggs pass 
into it. When it reaches the ninth and tenth, sperm 
cells obtained from another worm pass into it. It con- 
tinues to pass forward until it slips over the head. By 
contraction the ends close; a capsule has then been 
formed which contains sperm and eggs belonging to dif- 
ferent individuals. They unite and cell division and 
differentiation follow. 

Classification. — The Vermes, or worms, are a large 
group of animals that differ from each other materially. 
Their bodies are elongated and bilaterally symmetrical, 
with a marked distinction between the dorsrd and ventral 



VEEMES 171 

surfaces. There is no internal skeleton and the appen- 
dages are not jointed. They are divided into four 
classes, the flat worms, the round worms, the segmented 
worms, and the molluscoidea. These groups differ from 
each other so much that it is probable that their asso- 
ciation is an artificial grouping made for convenience. 

Flat Worms. — The flat worms may be free, living in 
water or moist earth, or parasitic. The body is flattened 
and has no appendages. There is no body cavity sepa- 
rate from the digestive system. In lower forms the 
alimentary canal has only one opening. In parasitic 
forms the alimentary tract may be completely lost. 
There is a small dorsal brain, and two nerve cords run 
backward parallel to each other. Eyes may be present 
on the dorsal surface near the brain. Some of these 
worms reproduce by fission. A new mouth appears, the 
body contracts in front of it and finally divides into two 
worms. Before one division is complete new divisions 
may begin, until a chain of as many as eight worms may 
be hanging together. There is also a sexual reproduc- 
tion. The parasitic forms are often responsible for 
disease in man and other animals. They enter the 
body in the food or water. The tapeworm is of these 
perhaps the best known. 

Round Worms. — The round worms are long, and as 
the name indicates, cylindrical, and the surface is cov- 
ered by a tough cuticle. The alimentary canal opens to 
the outside at both ends. Some forms live in water and 
some are parasitic in plants and in animals. Trichina 
is particularly dangerous. It enters the body in un- 
cooked pork. 



172 PHYSIOLOGY 

Segmented Worms. — The segmented worms have al- 
ready been fully described. Some of them are free and 
some live in tubes. Some live in the water and have 
well-developed heads bearing tentacles and eyes. Fleshy 
outgrowths on the surface of the body are used for 
swimming. The young undergo a metamorphosis simi- 
lar to that of the molluscs. Leeches have sucking discs 
and they have been used by physicians to draw blood 
from the body when it was thought that a disease might 
be cured by weakening the patient. 

Molluscoidea. — The molluscoidea were once thought 
to be molluscs. They have an alimentary canal that is 
open at both ends and there is a circle of tentacles around 
the mouth. Some of them produce large colonies by 
budding. Some have a bivalve shell through which a 
stalk projects which is fastened to some support. All 
of them reproduce sexually. 



CHAPTER XII 
ARTHROPODA 

External Characteristics.— The Arthropoda include a 
great number of apparently divergent forms such as lob- 
sters, spiders, flies, but their common characteristics are 
well-defined. The name means jointed-foot, and the 
class includes those animals which have an external 
jointed skeleton and jointed appendages. As in the 
segmented worms an evident external segmentation is 
associated with an internal segmentation, that is, the 
body is divided into a series of segments each of which 
contains parts of the internal organs. Many of the seg- 
ments are modified, however. Some of them are over- 
developed, some are under-developed and some are 
fused. The result is that different regions in the body 
become marked off, and it is not always easy to deter- 
mine the number of segments that are involved. Usu- 
ally three regions may be distinguished, the head which 
has well-developed sense organs, the thorax which bears 
the organs of locomotion, and the abdomen which may, 
or may not, bear appendages and may, or may not, 
show marked segmentation. 

Nervous System. — These animals are highly devel- 
oped and their tissues well differentiated. They are very 
irritable and respond readily to outside stimuli through 

173 



174 PHYSIOLOGY 

a well-developed muscular and nervous system. The 
nervous system is similar to that of segmented worms. 
It is made of a double ventral chain of ganglia con- 
nected with a nerve cord that divides at its anterior end, 
passes around the alimentary canal and unites on the 
dorsal side in a concentration of ganglia called the brain. 
Each segment contains a single ganglion which sends off 
two pairs of nerves to control the muscles and other 
organs of that segment. When the segments become 
fused the ganglia often become fused, but it is possible 
to determine the number of segments involved by count- 
ing the nerves that are given off. 

Digestive System. — A well-developed alimentary ca- 
nal open at both ends to the outside extends the length 
of the body. A large liver furnishes digestive juices. 

Respiratory System. — Special organs are set apart for 
respiration which take the form of gills in those animals 
that live in the water and trachea, or air tubes, in those 
that are surrounded by air. The gills are outgrowths of 
the body wall covered with a thin, moist membrane 
and permeated with numerous blood vessels. Oxygen 
dissolved in the water and carbon dioxide in the blood 
pass readily through the membrane. Tracheae are tubes 
which permeate the body and become filled with air. 
Oxygen can pass from the air in these tubes into the 
blood or directly into the tissues. 

Excretory Organs. — There are two kinds of excretory 
organs, both of which take the form of tubes. The neph- 
ridia, sometimes called the green gland, or shell gland, 
are in the anterior part of the animal and open to the 
outside. The Malpighian tubes present in some forms 



ARTHROPODA 175 

in great numbers open into the posterior part of the ali- 
mentary canal. 

Circulatory System. — The circulatory system is more 
highly developed in some forms than in others, but it is 
never entirely closed. A heart lies dorsal to the ali- 
mentary canal. The blood passes from it through the 
arteries into great open spaces and from these it is 
sucked back into the heart through large openings. 
There is an intimate connection between the develop- 
ment of the respiratory and circulatory systems. The 
more localized the respiration, the more complete the 
circulation ; the more it is diffused through the body the 
more closely oxygen is brought in contact with the tissues 
and the more the circulatory system is reduced. 

Sense Organs. — Most of these animals are sen- 
sitive to sound vibrations and seem able to distinguish 
substances through taste or smell ; but touch and sight 
are the most highly developed of the senses. The eyes 
are of two kinds, simple and compound. The compound 
eye is a collection of simple eyes closely united. Each 
simple eye sees part of the object. It is a tube with 
a sensitive surface at its base. The light from a single 
point is reflected through the tube and forms an image 
on the surface. The sum of the partial images makes 
the complete image. 

Reproduction. — Reproduction takes place sexually. 
Sometimes individuals are hermaphroditic, in which 
case eggs and sperm are formed in the same animal ; but 
usually the sexes are separate and to be distinguished 
by a difference in such external characters as color, size 
and form of appendages. The sexual organs are well- 



176 PHYSIOLOGY 

developed and open to the outside through ducts that are 
probably modified excretory organs. The development 
of unfertilized eggs occurs in bees and a few other forms. 
In aquatic forms eggs and sperm meet in the water; 
but in aerial forms union of the reproductive cells takes 
place in the duct of the female. 

Appendages. — The appendages are primarily loco- 
motor in function, but they may be modified into sense 
organs, into chewing jaws or into false feet. The 
false feet serve as gills, as supports for gills, as places 
for the attachment of eggs, as organs for the transfer of 
sperm, or as swimming or creeping organs. The head 
bears the antennae., or touch organs, the jaws and maxil- 
lipeds; the thorax, the true feet; and the abdomen bears 
the false feet or it lacks appendages. 

Classification. — The Arthropoda are divided into four 
classes: the Crustacea, the acerata, the insecta, and the 
myriapoda. 

The Crustacea. — In the Crustacea, gills are present, 
the feet are two-branched, and the reproductive ducts 
open near the middle of the body. They are divided into 
two classes, the first of which includes very small forms 
mostly microscopic whose bodies vary in the number of 
segments and in their appearance. The others are larger 
and their bodies consist of twenty segments. The best 
known examples are the shrimps, lobsters and crabs so 
much esteemed for food. Most of them are marine, but 
some live in fresh water and some live on land. 

Locomotion of the Lobster. — The study of the Lob- 
ster (Fig. 98) is interesting because it so well illus- 
trates the characteristics of the class and because it is 



AKTHROPODA 



177 



large enough to show the distinctive features without dif- 
ficulty. It moves through the water by contracting the 
tail or abdomen. This part of the animal is sharply 
segmented and the plates of which it is composed slip 




Fig. 98.— Anatomy of crayfish. A, dorsal surface removed ; B, scheme of circula- 
tion ; C, viscera removed, showing green gland and nervous system, a, anus ; 
aa, hepatic artery ; ae, antenna ; ai, antennula, also sternal artery ; am, muscles 
of stomach; oo, ophthalmic artery ; ap, abdominal artery; av, ventral artery; 
bl, urinary bladder ; br, gill arteries ; c, oesophageal commissures ; gd, green 
gland ; g?i, brain, ventral ganglia ; h, heart ; hd, intestine ; £, mandibular mus- 
cles ; 1,1', liver and its duct ; in, stomach ; o, otocyst ; ces, oesophagus ; on, optic 
nerve ; pc, pericardium ; sgn, sympathetic nerve ; t,t', testis or spermary ; v, ven- 
tral blood sinus; vd, sperm duct; idr, veins from gill to heart. (From Hertwig ) 

over each other so that when the animal flaps its tail 
a sharp bend takes place and the water is pushed ahead 
of it. At the same time the appendages move toward 
the head so that resistance is lessened and the animal 
moves rapidly backward. It spends a large part of its 
time on the rocks and moves over them very easily by 
means of the walking legs. 



PHYSIOLOGY 



The joints in these legs are all hinge joints, but there 
are four or five in each leg and they are so arranged 
with reference to each other that the leg has the power 
of turning to the mouth. A rotary motion is thus pos- 
sible comparable to that given by a single ball and 
socket joint to the human arm. These walking legs help 
to catch food and carry it to the mouth, where the heavy 

jaws crush it (Fig. 99). 
^\-v ? 111 rf \n These animals are great scav- 

v ^—^" engers, they eat organic 

material that contains the 
five food substances. 

External Characteristics. 
— The mouth at the ante- 
rior end of the body on the 
ventral side, the anus in the 
posterior end, and the repro- 
ductive openings on the base 
of the third or fifth pair of 
walking legs, are easily dis- 
tinguished. The sense or- 
gans are very prominent, 
long antennce and antennules, 
very sensitive to touch, and 
curious eyes elevated on 
stalks. On the base of the 
antennules are small open- 
ings that lead into organs 
sensitive to vibration. These are little sacs lined with 
sensory cells each of which bears a hair. Upon these 
hairs is balanced a tinv mass of calcium carbonate whose 




Fig. 99.— Appendages of the cray- 
fish. 1, first antenna ; 2, mandible 
3,4, first and second maxillae; 5, 
6,7, maxillipeds ; 8, walking leg 
9, pleopod. (From Hertwig.) 



ARTIIROPODA 179 

slightest motion is communicated by the hairs to the 
cells. 

Moulting of the Shell. — As the shell is hard and does 
not allow for growth it is moulted or cast off at intervals 
in order that the animal may grow larger. As soon as 
the hard coating is off, the animal at once expands ; the 
tender skin which is thus exposed hardens after a time, 
and the process is repeated. The new skin repeats every 
peculiarity of the cast shell so that the surface marking 
remains the same. Crabs are found in great numbers 
immediately after they have shed the shell and in this 
condition are called soft-shelled crabs. Other forms are 
not found in this condition in sufficient numbers to make 
them important commercially. 

Digestive System. — On the dorsal surface the ali- 
mentary canal extends the length of the body. At the 
anterior end it dips sharply and opens through the 
mouth on the ventral surface. At the dip is an enlarged 
stomach with hard walls that grind the food and pass 
it on into a softer stomach which digests it. If the ani- 
mal is freshly killed contractions may be seen, pass- 
ing like a wave the length of the intestine and forcing 
the contents toward the posterior end. 

Other Organs. — Near the anterior end of the lobster 
are two nephridia-like excretory organs, called the green 
glands, which give off the waste from the protoplasm. 

Two very prominent brownish glands act as a liver 
and pour digestive juices into the alimentary canal near 
its anterior end. 

The heart, situated on the dorsal side, is a curious 
pentagonal structure with blood vessels passing off from 



180 PHYSIOLOGY 

the corners. On its surface are large openings through 
which the blood re-enters the heart from the spaces into 
which it is poured. The blood is uncolored. It very 
quickly coagulates if a vessel is cut. 

Underneath lie the large muscles used for food. They 
almost fill the abdomen and their segmental arrangement 
is evident at a glance. Their contraction gives the abdo- 
men the powerful stroke by means of which a passage is 
forced through the water. 

Respiration. — As the lobster is covered with a hard 
shell, a specialized moist membrane has been set aside 
for breathing. This membrane is confined to the sur- 
face of the gills, which lie under the free edge of the 
shell. Water is kept running over them by an appen- 
dage which moves in such a way that it causes a 
current. Oxygen is thus able to pass from the water 
through the thin gill membrane into the blood and 
carbon dioxide is able to pass from the blood into the 
water. 

Reproduction. — The reproductive organs are very 
prominent, especially in the breeding season. The sexes 
are separate. The eggs pass out of the body through 
ducts that open usually on the base of the third (fe- 
male) or fifth (male) walking foot and are held by the 
swimmerets, or appendages of the abdomen. While there 
they come in contact with sperm and begin their develop- 
ment. They remain there until the eggs are hatched 
and the young can shift for themselves. The little 
larvae are unlike the parent but soon undergo the change 
which gives them the adult form. 

Segmentation. — The nerve cord lies on the ventral 



ARTHROPODA 181 

surface. As in the earthworm it has a ganglion and a 
pair of nerves for every segment. At the anterior end 
it passes around the alimentary canal in a ring. On the 
dorsal and ventral sides the juncture of the two parts 
forming the ring is marked by a concentration of gan- 
glia. The number of ganglia involved may be found by 
counting the number of nerves given off. The total num- 
ber of ganglia corresponds with the number of pairs of 
appendages and with the number of segments, so that the 
internal evidences of segmentation are in harmony with 
the external sign. It will be found exclusive of the eyes 
to be twenty. 

Acerata. — The acerata lack antennae. The body is 
divided into two parts, the cephalothorax which bears 
six pairs of appendages, and the abdomen which is with- 
out appendages. They breathe through gills, lungs or 
trachea, and the reproductive ducts open near the mid- 
dle of the body. The best knowm representatives of the 
group are the scorpions, spiders, daddy-long-legs, ticks, 
mites, etc., that are such pests. In the spiders the cepha- 
lothorax and the abdomen are unsegmented externally 
but they are sharply separated. In front are the poison 
jaw r s and on the tip of the lower surface of the abdomen 
are two or three pairs of spinnerettes. These give off 
a fluid which hardens when exposed to the air. This is 
used to protect the eggs and to form the web that is used 
as a home and as a trap for prey. 

Myriapoda. — To this group belong the centipeds and 
the millipeds. In it there is no distinction between the 
thorax and abdomen. The head is well-defined and 
is succeeded by a long series of segments which bear one 



182 



PHYSIOLOGY 



(centipeds), (Fig. 100), or two (millipeds), (Fig. 101), 
pairs of appendages. 

Insecta. — (Hexapoda). — The study of insects is a 
science in itself. There are supposed to be more than 
a million distinct forms and more species than in 

all the rest of the animal king- 
dom. The body is divided into 
three distinct regions. The head 
bears the antennse, the sense or- 
gans and the mouth parts. These 
are fitted for biting or for suck- 
ing. The thorax is made of 
three segments which may be 
movable. On it are three pairs 
of legs, and usually two pairs of 
wings, but these may be entirely 
missing or one pair may be re- 
duced or hardened. The ab- 
domen is made of ten segments, 
though the number may be re- 
duced. It may be fixed to the 
thorax by its entire width or by 
a slender stalk. It may have 
three pairs of appendages, but 
these are never locomotor in the 
adult. They may be rudimen- 
tary or they may be transformed into the organ which is 
used for laying the eggs or for stinging. The sexes are 
separate. 

The alimentary canal has few convolutions (Fig. 
102). There is a chewing stomach and a true stomach. 




Fig. 100.— Centiped. 



AETHROPODA 



183 



The excretory organs take the form of Malpighian 

tubules which vary in number from two to a hundred. 
They open into the intestine. 

The circulatory organs are poorly developed, but they 
are compensated for by the tracheae. The number of 
tracheal openings on the side of the thorax and abdomen 
varies from three to ten, but there are never more than 
one for each segment. They branch 
internally again and again until the 
fine branches permeate every part of 
the body. Sometimes they are en- 
larged into air sacs which make the 
body light. Air is drawn in by a 
rhythmical enlargement of the abdo- 
men and reaches all the tissues of the 
body. It is expelled again by the 
contraction of the abdomen. 

The alimentary canal passes be- 
tween the two halves of the nerve 
cord which unite to form a dorsal 
ganglion, or brain, and a ventral 
cord. The eyes, simple and com- 
pound, are on the head. The organs 
for hearing may be on the base of the abdomen, on the 
legs or on the antennae. Taste is on the lower lip and 
smell on the antennae. 

When the young leave the egg they are very small; 
they may have the adult appearance, or they may be like 
the adult except that the wings are small and later in- 
crease in size with every moult, or they may be entirely 
different from the adult, in which case they undergo a 




Fig. 101.— Milliped. 



184 PHYSIOLOGY 

larval metamorphosis. The larva is very active and eats 
voraciously, it molts again and again and then becomes 
quiet. During the quiescent stage it eats nothing, for 
important changes occur with which eating would in- 
terfere. Through these changes the adult form is gained. 
The insects are divided into nine classes. The well- 
known forms that represent them are: (1) The silver 




Fig. 102.— Diagram of the anatomy of an insect, b, brain ; c, crop ; h, heart ; m, 
Malpighian tubes ; r, reproductive organs ; 5, stomach ; sg, salivary glands ; v, 
ganglia of ventral chain. (From Kingsley.) 

fish, which eat paper and starched clothing; (2) Grass- 
hoppers, crickets, locusts, which may damage crops 
almost incalculably; (3) Dragon flies, may flies; (4) 
Caddis flies and ant lions; (5) Flies, mosquitoes, pests 
and carriers of disease; (6) Beetles, lady bugs, buffalo 
bugs; (7) Ants, bees and wasps; (8) Seventeen-year 
locust; (9) Moths and butterflies, whose larvae often 
damage crops. 



CHAPTER XIII 
VERTEBRATA 

Irritability. — In vertebrates (e.g. fish, birds, elephants, 
human beings) as in all other animals the physiological 
manifestations are those that distinguish the simplest 
forms of living matter, irritability, assimilation, repro- 
duction, and in this group as in all the others the spe- 
cial method of manifestation depends on the structure. 

Vertebrates are distinguished from other animals by 
the possession of an internal skeleton with a spinal col- 
umn. This furnishes the framework for the body and 
helps to preserve the form of the animal. The bones are 
capable of co-ordinated movement through the irrita- 
bility of the attached muscles. When a muscle con- 
tracts it becomes shorter and thicker; its two ends ap- 
proach and the bones to which it is attached approach. 
The stimulus which moves the muscle is usually carried 
to it by nerves which are very sensitive. They conduct 
a stimulus more quickly than any other form of proto- 
plasm, and through their intervention the muscles act 
more quickly than they would otherwise act. 

Assimilation. — Assimilation takes place in vertebrates 
as in all other animals, but the alimentary canal and its 
appendages are more highly developed. For food they 
need carbohydrates, fats, proteids, water and salts, 

185 



186 PHYSIOLOGY 

and these they gain very readily from the substances 
which they eat. The canal is definitely divided by 
enlargements and constrictions into the oesophagus, the 
stomach, the large and small intestine. Time and space 
for the digestion and absorption of food are afforded 
by the length of the intestine, which is coiled in the abdo- 
men. The pancreas and liver are large glands con- 
nected with the canal which aid in forming digestive 
juices. The kidneys excrete the nitrogenous waste. 

Respiration. — In higher forms the body cavity is 
divided by the diaphragm into two parts. In the upper 
part the lungs are situated. The lungs correspond to the 
gills of aquatic forms. They are composed of a thin 
membrane arranged to form air sacs, in which blood ves- 
sels are situated. Air from outside enters the air sacs 
and comes in contact with the moist membrane of the 
lungs ; oxygen passes into the blood and from the blood 
into the cells of the body. Carbon dioxide passes from 
the cells into the blood and from the blood to the air in 
the lungs, thence to the outside. The entire process 
depends upon the law by which gases move from 
a place of high pressure to a place of low pressure. 
The 'air enters the lungs because the pressure is reduced 
there by the sudden enlargement of the chest cavity 
caused by the contraction of the diaphragm and the 
elevation of the ribs. Oxygen enters the cells because 
its pressure is reduced in the cells through its use in 
the manufacture of protoplasm. 

Reproduction. — The reproductive organs are very 
prominent, especially in the breeding season. In verte- 
brates reproduction is sexual and depends on the union 



VERTEBRATA 187 

of two dissimilar cells. In most aquatic forms, eggs 
and sperm are turned loose in the water. They unite 
and the new cell divides and differentiates until an ani- 
mal like the parent is formed. In higher animals, or 
rather in land animals, the process is similar, except that 
the cells cannot be turned out in the air, where they 
would die, but unite in the tube which leads from the 
ovary to the outside. There they develop to a greater 
or less degree before they pass to the exterior. 

General Characteristics. — There are no external signs 
of segmentation in the vertebrates, but the internal parts 
are arranged with special reference to the segmented 
vertebral column and spinal cord. 

Except for localized hardening of the skin found, for 
example, in the scales of fish and reptiles, or in the 
hoofs and nails of other forms, there is no external 
skeleton. There is, however, an internal skeleton con- 
sisting of a skull and spinal column which supports ap- 
pendages, sometimes unpaired but usually paired. 

The central nervous system, consisting of a brain and 
spinal cord, is dorsal in position. The sense organs are 
w r ell-developed, especially the eyes and the ears. 

Gills are present in aquatic forms, lungs in terres- 
trial forms. Gill slits are present in them all, but they 
are lost in higher forms in adult life. 

The circulatory system is closed. The heart lies 
ventrally in the pericardium. It is divided into an auri- 
cle and ventricle in gill-breathing forms, and contains 
only venous blood. When lungs are present it is fur- 
ther subdivided into right and left halves so that arterial 
is separated from venous blood. 



188 PHYSIOLOGY 

The development of the alimentary canal depends 
upon the character of the food that is eaten and the 
length of time that is necessary for its digestion. In all 
forms it is a tube open at both ends to the outside, with 
one or more definite enlargements. It is too long to pass 
directly through the body and is therefore much coiled. 

Reproduction is strictly sexual and the sexes are 
usually separate. The excretory ducts usually act as 
ducts for the reproductive organs. 

Classification. — The vertebrates are divided into: 

Pisces or fish; aquatic forms breathing by gills, 
usually covered with scales. The venous heart is divided 
into an auricle and a ventricle. 

Amphibia, e.g. frogs; aquatic forms usually hav- 
ing true feet. The heart is divided into two auricles and 
a ventricle. A metamorphosis is common. Bushy, 
external gills are present in the young; lungs in the 
adult. These may persist together or they may succeed 
each other. 

Reptilia, e.g. snakes, turtles ; having strongly ossified 
skeleton and cornified skin. The heart is divided into 
two auricles and two incompletely separated ventricles. 
They have no functional gills. 

Aves or birds; warm-blooded animals having wings 
and feathers. The four-chambered heart is completely 
divided into right and left halves. 

Mammals, e.g. cows, dogs, human beings; warm- 
blooded animals with hairy skin, four-chambered heart, 
highly-developed teeth having roots. Very low forms 
lay eggs ; others bring forth their young alive. The 
young are nourished by milk, 



CHAPTER XIV 
PLANTS 

Irritability. — As plants as well as animals are com- 
posed largely of living matter, they as well as animals 
manifest the physiological qualities of living matter, irri- 
tability, assimilation, and reproduction, and the mani- 
festation is governed by the same physical and chemical 
principles. To understand, then, the life history of any 
individual plant, its irritability, assimilation, and repro- 
duction must be studied in relation to its structure, upon 
which the peculiar way in which they manifest them- 
selves is dependent. 

Plants are very irritable. Within the cell the proto- 
plasm is in constant motion. In addition many of them 
are able to move as independent organisms. Lower plants 
through the activity of cilia move readily from place to 
place. Higher plants are usually firmly fixed, but they 
respond readily to external forces such as heat, light or 
gravity, and bend the whole or a part of the body in the 
direction of the acting force. Any number of illustra- 
tions might be mentioned such as the twining of the 
tendrils of peas, the snapping together of the valves of 
venus fly-trap, the turning toward the sun of helio- 
trope, the shrinking of a sensitive plant, and the droop- 
ing of the leaves of oxalis. 

189 



190 PHYSIOLOGY 

Assimilation. — The assimilation of plants involves the 
transformation of water and carbon dioxide into starch, 
the use of starch, oil, mineral substances in forming pro- 
toplasm, the disintegration of protoplasm, the giving 
off of waste in the form of water and carbon dioxide, and 
the passage of these products throughout the plant. If 
a branch bearing leaves is enclosed in an air-tight jar 
the water that is given off may be caught on the sides 
of the jar. If a branch is enclosed with a dish of lime 
water the carbon dioxide given off in the process of 
breathing will turn the linle water milky. Oxygen given 
off in the formation of starch may be caught by inserting 
a funnel over a mass of water plants exposed to the 
sunlight. 

Reproduction. — Reproduction is both sexual and non- 
sexual, as it is in animals. In non-sexual reproduction, 
fission, budding, growth from cuttings take place ; while 
in sexual reproduction two dissimilar cells unite and the 
new cell divides and differentiates until a new organ- 
ism is formed. There is a most remarkable connection 
between the sexual and non-sexual methods of repro- 
duction, not unlike the alternation of generations found 
in the jellyfish, where a non-sexual generation produces 
a sexual generation and the sexual generation in turn 
produces a non-sexual generation. In plants, however, 
this is not a more or less isolated case. It progresses 
steadily from low flowerless plants to the flowering 
forms. At first the sexual generation is prominent and 
the non-sexual generation very insignificant as in the 
liverworts. Later, by a series of gentle gradations, 
the non-sexual generation becomes prominent and 



PLANTS 191 

the sexual insignificant, as in the ferns and flowering 
plants. 

The activity of plants as of all organisms may 
thus be reduced to the effort of protoplasm to mani- 
fest its inherent properties — irritability, assimilation, 
reproduction. 



APPENDIX 

To the teacher who is quite satisfied with her own 
method the author does not venture to make suggestions. 
If she is efficient she does not need them, if she is not, 
she would not know how to make use of them if they 
were offered. To the young and enthusiastic body of 
women who have feelers out in all directions for any- 
thing that may be made to serve them, the author can 
not refrain from saying a word. 

There is no profession so nerve-racking and so deaden- 
ing as teaching unless the teacher has a viewpoint that 
keeps her interest perennially fresh. The subject- 
matter itself is not sufficient, for no matter how alive 
it may be in the beginning it will become dead after 
it is repeated, as sometimes happens, two or three times 
in one year and a single lesson four or five times in 
one day. There is an unfailing source of interest, how- 
ever, in the minds of the pupils. Every change of class 
brings fresh minds to work upon and the reaction of a 
thought upon these minds is vitally interesting. 

In the course of a month a teacher may come to know 
the way in which her pupils look at things so well that 
she can predict whether an individual will be able to 
answer a question and just what answer he will give. 
This is of infinite importance in presenting a subject 
to a class. A fact may not be interesting in itself, it 

192 



APPENDIX 193 

may not be of the least value to a child in itself, but the 
way in which he looks at it and the way in which he 
relates it to other facts is supremely important. 

Facts as facts are worth very little, they may be so 
much dead weight. A teacher who simply imparts 
facts wastes her time, and what is more important, she 
wastes her pupils' minds. The facts are forgotten and 
the mind is unawakened. The great thing, the child's 
mental growth and development, is unaccomplished. 

There has been much unprofitable discussion over the 
educative value of different subjects, and mathematics 
and the classics have warred with each other for the 
first place. But every subject has educative value. 
Every subject can be made to appeal to the reasoning 
power if it is properly handled, and children like to 
reason. They like the sensation of using their own 
minds, when the privilege is accorded them. They are 
always wondering about things and they are always 
asking questions if their curiosity has not been stifled 
by inconsiderate grown people and they have not found 
their asking unprofitable. 

One thing that a teacher should do for a child in 
her care is to preserve his legitimate curiosity and 
foster his reasoning faculty. No subject is better fitted 
for this than physiology, for it is closely related to other 
subjects, and is full of causal relations. A good teacher 
who knows her subject, and a few other things, can not 
help correlating it with everything in the universe that 
has come w T ithin her ken that will help her pupils to 
grasp an idea or follow a chain of reasoning. 

The first thing, then, is know your subject, not simply 



194 PHYSIOLOGY 

know a few things about it. Then see that you are 
interested in the way that your pupils take hold of it. 
Vary your method. There is nothing so deadly as 
monotony. Do the unexpected, not by way of torment- 
ing your pupils with unexpected quizzes full of catch 
questions, but by way of illuminating the subject. I 
once heard a little girl exclaim as she left a classroom: 
"I like to come to this class. It is like a play; I 
don't know what is going to happen next." And yet 
good hard work was done in that class. It was not 
simply an entertainment provided by the teacher. 
Too much of that is done, and it is an unprofitable 
proceeding. 

Use the inductive method. Ask questions and ask 
them well. There is no asset so valuable to the teacher 
as the ability to ask good questions, and the instinct, or 
knowledge of her pupils, which leads her to ask the right 
question, at the right time, of the right pupil. By 
judicious questioning the amount that is told him may 
be reduced to a minimum. 

A teacher who tells a pupil anything that he can find 
out for himself deprives him of two rights, the joy of 
discovery and the grasp of the fact that comes with 
discovery. Before one really knows a thing one's own 
mind must discover it. The questions should make the 
pupil think, should force him to keep the relationship 
of details in his mind and make broader and broader 
comparisons. It is possible to rob the examination of all 
its terrors if the pupil is made to understand that the 
object of questioning is not to find out what he knows, 
but by extending the viewpoint from details to a com- 



APPENDIX 195 

prehensive view of the entire subject, to teach him 
something that he does not know. 

Sometimes it is much more valuable to have a pupil 
fail to answer a question than to have him answer it. 
Especially if the question is held in reserve until by a 
series of other questions that lead gradually from one 
thing to another the pupil suddenly finds that " he knew 
it all the time." It is possible in this way to teach a 
pupil to think for himself by making him see the ques- 
tions that he must ask himself, one at a time, until the 
last one is so simple it presents no difficulty. 

The ability to ask good questions means a grasp of a 
subject, therefore foster the question-asking habit in the 
pupils. Set apart a day in the week w T hen they may 
ask anything they want to ask. Most children seem to 
lose the question-habit as they grow older. It is a bad 
sign. Reawaken it if possible, only do not tolerate a 
thoughtless question. Children know very well when 
they are asking a question merely for the sake of 
talking. 

The experiment w r as tried wdth a class of first-year 
high school pupils in botany. A month was spent in 
establishing a viewpoint. Then, except for the occa- 
sional laboratory periods and special discussions, the 
classroom time was spent by the pupils in asking about 
anything that interested them. Occasionally they wan- 
dered far afield but never so far that the subject intro- 
duced could not be made subservient for illustration. 
The hour w T as a delight. Superstitions were weeded out 
and light was let into dark corners. Sometimes the 
questions were answered, sometimes they were kept for 



196 PHYSIOLOGY 

a more seasonable time, sometimes they were unanswer- 
able. But there was no difficulty about correlation. 
Every subject that could be correlated with botany was 
touched upon and many hazy points cleared that had 
been left over in other subjects. And the teacher never 
turned out a class which in the same time had absorbed 
so much botany, and whose members were so well able 
to make observations and draw their own conclusions. 

Such a method reacts on the teacher. Her mind can 
not grow stagnant, it has to be alert or she will be 
caught fatally napping. And she learns very quickly 
that nothing is gained by pretense. Sooner or later 
" bluffing " will cost her the children's confidence and 
respect. If she does not know a thing it is safest to 
confess ignorance. If she has a sufficient mental equip- 
ment she can afford to forego the pretense of omni- 
science. 

Since the introduction of laboratory work in the 
schools many teachers have been blinded by its obvious 
advantages and have allowed it to usurp the place of 
a more important phase of the work. It is introduced 
in so many subjects and takes so much time that, to 
accomplish the tasks set him, the pupil spends all of his 
time working in the laboratory and transcribing the 
results in a notebook. The result is that he gets no 
chance to think over what he has seen or done, and 
digest it in his mind. Laboratory work is of no value 
unless it is made a suggestive basis for mental excur- 
sions and unless the suggested thoughts are seized upon 
and made to crystallize. 

To study a section of potato takes the average pupil 



APPENDIX 197 

about four hours, but to understand what it suggests 
takes three or four weeks. Practically only two things 
are to be seen, many transparent globules and definitely 
arranged lines which enclose the globules. A young 
student sees these things and can make a very creditable 
picture of them, but if he is questioned it will be found 
that his idea of the meaning of his sketch is very hazy. 
He should not be forced to go on, then, until his difficul- 
ties have been cleared away and the suggestiveness of 
the section has been exhausted. 

He may know, in a general way, that the potato con- 
tains starch and that cells are to be seen with the help 
of the compound microscope. But it is fatal to a real 
interpretation of what he sees if he is allowed to use 
these words before he is sure of their meaning, for he 
is apt to use them indiscriminately. It is much better 
for him to use some non-technical word in the beginning 
that simply describes what he sees. It matters very 
little if he calls the cell w^alls, lines, and the starch 
grains, globules, if he is able to find out for himself that 
the lines are the walls of a box that enclose the globules 
and that both lines and globules are insoluble solids. 
The premature use of a word or a phrase to clothe an 
idea that is not perfectly clear means the raising of a 
barrier which may entirely prevent or indefinitely delay 
perfect understanding. It is often wise to use a cir- 
cumlocution to express an idea until one is sure of 
using the word without losing sight of the thought. 
Carelessness in the use of words re&ults in such very 
absurd ideas and so. much is gained in mental power 
by accuracy in using them that it is surprising to find 



198 PHYSIOLOGY 

how little attention is paid to this phase of school work. 
A new word is often learned before the idea which it 
embodies is fully grasped, or the idea slips away, and 
the word comes to be substituted for the idea. It is then 
used at random, singly or associated with other words in 
catch phrases, without a vestige of the underlying mean- 
ing in the mind. 

Such simple words as solid, liquid, gas, heat, com- 
bustion, chemical, physical, etc., are often used with so 
little understanding of their real meaning, that one is 
blinded to perfectly obvious relations. A word is sup- 
posed to be the sign of an idea, but words are often used 
to cover up a deartri of ideas. Even the wisest of us 
is apt to fall into this shiftless habit, and it is no mean 
offense, for it is a sign that one is falling into a lazy 
habit of mind. It means finally the loss of mental alert- 
ness and the joy of using one's own mind, which, after 
all, is one of the greatest joys one can have. 

Even at the risk of being too diagrammatic it is 
sometimes worth while to put the ideas that very simple 
words stand for in a form which can be readily 
visualized. By visualizing the meaning of the long 
familiar word heat, for example, it may be made to 
assume a new force and to bring ideas which have been 
hazy or unconnected into a logical and definite relation. 
Heat transference, expansion, evaporation, should not 
be isolated ideas, but very definite corollaries of the 
fact that matter is made of molecules which move and 
have spaces between them. A pupil may understand 
such a series of ideas and yet not be able to apply 
them to the explanation of even simple phenomena. 



APPENDIX 199 

With a little help, however, in a few specific instances 
he will gain the power of making the application for 
himself, and one of the great aims of school teaching 
will be realized. A pupil who can use what he knows 
effectively has really made progress educationally, but 
if he can do nothing but remember what someone else 
has told him, he is outside the field of mental interest. 
This method may sometimes seem discouragingly slow, 
but time is never lost if it is used so that in the end the 
pupil is ready to think and ready to find thinking 
interesting. 



REVIEW QUESTIONS 

These questions are not intended for consecutive classroom 
use. Neither is it intended that the pupil shall turn to any spe- 
cific page for an answer. When he has completed the book he will 
find that he w T ill be able in most cases to answer the questions 
without reference to the text and that his effort will be an easy 
method of review. 

1. Explain evaporation without using the word heat. 

2. What has evaporation to do with human physiology? 

3. In w T hat way is the economical principle of division of labor 
exemplified in the development of animals ? 

4. Why (physiologically) does a dog pant? 

5. How is the same result accomplished in human beings? 

6. Does anything similar happen in frogs ? Explain. 

7. Should toads be killed or preserved? Earthworms? Cater- 
pillars? 

8. Is it necessary to chew r soft foods? 

9. Trace the digestion and absorption of a drop of milk. 

10. Why can we not commit suicide by holding the breath? 

11. Are the blood corpuscles living or dead? Are the white and 
red corpuscles composed of the same material? 

12. Are potatoes fattening? Explain. 

13. Mention a many-celled animal that does not have a cir- 
culatory system and explain what compensates for its lack. 

14. Does the blood flow faster in the capillaries or in the 
arteries? Explain. 

15. What is the physiological cause of blushing? 

16. When an earthworm is touched it crawls away, when an 
anemone is touched it merely jerks back close to its support. 
Explain physiologically and mechanically. 

17. To what physiological factor is the sensation of cold due? 

18. Why is it considered unsportsman-like to " hit below the 
belt"? 

201 



202 EEVIEW QUESTIONS 

19. Why should plants not be kept in the bedroom at night? 
Is the same thing true in the daytime? Explain. 

20. Muscular exercise is a source of heat. Why can not fever 
be produced by muscular exercise? 

21. Why does fanning a wet object help to dry it? 

22. How does it happen that too much exercise and too little 
exercise affect the body in the same way? 

23. What change takes place in a man's body as he ascends in 
a balloon? 

24. Why does watering the lawn make one feel cooler in 
summer ? 

25. Is there any physiological process in man comparable to 
regeneration in starfish? Think carefully. 

26. How does it happen that warm-blooded animals have a 
constant temperature? 

27. Give an argument against the idea that food is in the 
body as soon as it is swallowed. 

28. Is the curdling of milk comparable to any physiological 
process ? 

29. Describe the interdependence of plants and animals. 

30. Why does blood collect in the finger when a band is 
tied around it? 

31. Why does the foot of the crossed knee jerk if the knee is 
struck ? 

32. What causes fever? 

33. Show how the sexual reproduction of Vorticella is a con- 
necting link between the conjugation of a simple form like the 
Paramecium and the fertilization of more highly developed forms 
like the sea urchin. 

34. Show the relation between chemical action and human 
physiology by reference to the waste and repair of the body. 

35. How is heat produced in the bodies of plants and animals? 

36. Trace the development of the digestive system, using for 
examples the hydroid, jellyfish, starfish, earthworm, clam. 

37. Show how the characteristic movements of animals are 
dependent on their structure, using for examples the ameba, 
jellyfish, lobster, fly. 

38. Show the connection between muscular exercise and other 
functions of the body, particularly circulation and respiration, 

39. Explain the position of the diaphragm when relaxed. 



KEVIEW QUESTIONS 203 

40. Is there any relation between the sap in a cell from a 
flower hair and the starch in the potato cell ? 

41. Starch grains increase in size and also stream across the 
field of a microscope. How do these processes differ from the 
growth and motion of an ameba? 

42. Mention three processes in the human body dependent on 
the physical principle of equilibrium (balance of activity). 

43. In what way does the weight of the air affect the physiol- 
ogy of organisms? 

44. In considering the differences and the similarities of lower 
and higher animals, which seem to you the stronger factor in 
the development of the world as it is to-day? 

45. Is your respect for lower animals increased, or is your 
respect for man decreased by a consideration of the similarity of 
their bodily functions ? 

46. Is your respect for a higher power increased or decreased 
by a consideration of the laws that govern the physiology of 
organisms ? 

To compare two things is to point out both resemblances and 
differences. By bringing the general characteristics of two dif- 
ferent things into juxtaposition, the characteristics of both are 
fixed in the mind. Compare 

1. Living matter with non-living matter. 

2. Plants with animals. 

3. One-celled animals with many-celled animals. 

4. Lymph with blood. 

5. Arterial blood with venous blood. 

6. The constitution of milk with the constitution of blood. 

7. Fission with budding. 

8. Conjugation with fertilization. 

9. Sexual reproduction with non-sexual reproduction. 

10. The structure of a sea-anemone w T ith the structure of coral. 

11. The structure of a sea-anemone with the structure of a 
hydroid. 

12. The structure of an earthworm with the structure of a 
lobster. 

13. The symmetry of an earthworm with the symmetry of a 
starfish. 

14. The making of starch with breathing. 



204 REVIEW QUESTIONS 

15. Breathing by gills with breathing by lungs. 

16. The action of nerves with the action of muscles. 

17. The anal spot with the contractile vacuole. 

18. Scientific law with law of the land. 

19. The arm of a human being with the leg of a lobster. 



INDEX 



(Pages on which figures occur are indicated by heavy type.) 



Abalone, 159 

Abdomen, 74, 173, 176, 177, 
180, 181, 182, 183 

Absorption, 58, 64 

Acerata, 181 

Activity, 1, 2, 9, 46, 100, 131 

Air, 15, 19, 25, 29, 32, 33, 34, 
38, 40, 41 

Air cells, 34 

Air passages, 34 

Air pressure, 21 

Alcohol, 54, 84, 118, 119 

Alimentary canal (see Diges- 
tive tract) 

Alternation of generations, 145, 
146, 190 

Ameba, 11, 30, 78, 99, 124, 128, 
131 

Ameboid motion, 141 

Amphibia, 188 

Anal spot, 130 

Analysis, 53 

Anatomy, 1, 2, 3 

Angle worm (see Earth worm) 

Animals, 1, 2, 9, 27, 53, 125 

Antennae, 176, 178, 181, 182, 
183 

Antennules, 178 

Ant lion, 184 

Ants, 184 , 

Anus, 48, 49, 50 

Aorta, 72 

Aortic arch, 166 

Appendages, 173, 176, 178, 
180, 181, 182, 187 

Aquatic animals, 31, 33, 169 

Arm, 105, 106, 107, 108, 109 

Arteries, 71, 74 

Arthropoda, 173-184 

Assimilation, 45-66; of proto- 
zoa, 10, 11, 129, 130; of coe- 



lenterata, 139-141; of echi- 
nodermata, 151, 152; of 
vermes, 163-165; of verte- 
bra ta, 185, 186; of plants, 
190 
Associated movements, 110, 111 
Auricles, 69, 70, 72, 157 
Auriculo-ventricular valves, 71 
Aves, 188 

Axial skeleton (see Spinal col- 
umn) 

Backbone, 104 

Bad air, 44 

Ball and socket joint, 110 

Bees, 184 

Beetles, 184 

Beverages, 54 

Bilateral symmetry, 149, 152, 

155 
Bile, 58 
Birds, 185, 188 
Bladder, 60 
Blastula, 91, 92 
Blood, 31, 32, 43, 57, 76, 77 
Blood, composition of, 75, 80 
Blood, corpuscles of, 75-81, 99 
Blood plasma, 80 
Blood pressure, 116 
Blood, regulation of flow, 69-75 
Blood vessels, 32, 33 
Blushing, 83 
Body cavity, 147, 157 
Body temperature, 75, 82, 83 
Bones, 104, 185 
Brain, 112, 113, 173 
Branchiae (see Gills) 
Branchial hearts, 157 
Bread, 54 

Breakfast foods, 54 
Breathing (see Respiration) 



205 



206 



INDEX 



Bud, 133, 143 
Budding, 143, 145, 190 
Bugs, 184 

Burning (see Combustion) 
Butterflies, 184 

Caddis fly, 184 

Calcium chloride, 101 

Calcium carbonate, 143, 154, 
178 

Capillaries, 60, 72, 81 

Carbohydrates, 52, 53 

Carbon, 16, 17, 18, 52, 53 

Carbon dioxide, 13, 16, 17, 18, 
20, 22, 23, 28, 29, 30, 31, 32, 
40, 42, 43, 52, 60, 102, 132, 
141, 152, 157, 160, 174, 180, 
186 

Carnivorous animals, 51 

Cell, 8, 9, 20 

Cell-differentiation, 91, 152, 
187 

Cell-division, 91, 92, 152, 187 

Cell-wall, 9, 12, 15, 16, 20 

Cellulose, 52, 54 

Centipedes, 181, 182 

Cephalothorax, 181 

Cereals, 53 

Characteristics of living matter, 
7, 11, 21, 22, 87, 126, 185, 
189, 191 

Charcoal, 17 

Chemical action, 16, 18, 45, 58, 
131 

Chemistry, 2, 3 

Chest cavity, 37, 42, 72 

Chewing, 56, 57, 64 

Chiton, 155 

Chlorophyll, 18 

Chocolate, 54 

Cilia, 10, 99, 129, 155, 189 

Circulation of protoplasm, 43, 
67, 99 

Circulation of blood, 67-86 

Circulatory system, 67-75; of 
protozoa, 129; of coelenterata, 
141 ; of echinodermata, 68, 
147, 150; of mollusca, 157, 
158, 160; of vermes, 68, 165, 
166, 167; of arthropoda, 175; 



of insecta, 183; of vertebrata, 
187 

Clam, 49, 103, 155, 157, 159 

Classification of mollusca, 161; 
of vermes, 170-172; of ar- 
thropoda, 176-184; of verte- 
brata, 188 

Clitellum, 170 

Coagulation of blood, 79, 80 

Cocoa, 54 

Coelenterata, 135-146, 147, 152 

Coffee, 54 

Cold, sensation of, 84 

Colds, 83 

Collar bone, 105 

Colonial forms, 143, 144, 172 

Combustion, 16, 17, 18 

Compound eyes, 175 

Condiments, 54 

Conjugation, 88, 89, 132, 144 

Connective tissue, 76 

Constipation, 58 

Contractile vacuole, 132 

Contractility, 141 

Cooking, 63 

Co-ordination, 102 

Coral, 142, 143 

Coronary artery, 118 

Corpuscles, 75, 76, 77, 78, 79, 
80, 81, 99 

Cows, 188 

Crab, 176, 179 

Crayfish, 32, 177 

Crickets, 184 

Cross fertilization, 170 

Crustacea, 176 

Daddy-long-legs, 181 
Depressor nerve, 85 
Development, 94, 118, 136 
Devil fish, 161 
Diaphragm, 35, 36, 37, 38, 39, 

42, 44, 102, 186 
Diet, 50, 51, 53, 63 
Differentiation, 89, 92, 93, 97 
Diffusion, 14, 15, 22, 160 
Digestion, 55, 58, 62, 63 
Digestive juices, 55, 56, 57, 63 
Digestive tract, development of, 

47-55; of protozoa, 129; of 



INDEX 



207 



ccelenterata, 137-141; of echi- 
nodermata, 147, 141), 150, 
152; of mollusca, 158, 100; 
of vermes, 163-165, 171; of 
arthropoda, 174, 175, 179; of 
vertebrata, 186, 188 

Diphtheria, 80 

Disease, 79 

Disease germs, 40, 41, 52, 63, 
64 

Dissepiment, 168 

Division of labor, 30 

Dogs, 188 

Dragon flies, 184 

Drug, 54, 63 

Ducts, 150, 152, 176, 180 

Eating, method of, 11, 152, 

164 
Ear, 116 
Earthworm, 49, 68, 102, 112, 

162-170 
Echinodermata, 147-153 
Economic value of mollusca, 

159, 160; of vermes, 164; of 
Crustacea, 176, 178, 179, 180; 
of insecta, 184 

Ectoderm, 93, 135, 136, 141 

Egg-cell, 91, 92, 96 

Eggs, 145, 152, 169, 180 

Elasticity, 38, 72, 74, 75 

Elephants, 185 

Elements found in protoplasm, 

53 
Entoderm, 93, 135, 136, 141 
Enzyme, 19, 55, 56, 57, 64, 78 
Equilibrium, 25, 26, 27, 28, 29, 

38, 43, 56, 78 
Evaporation, 14, 15, 22, 83 
Evolution, 87, 94, 123 
Excretion, 59, 60, 130 
Excretory organ, 46, 47, 59, 60, 

160, 169, 174, 176, 179 
Exercise, 41, 83, 117 
Expansion, 14, 22 
Expiration, 38, 39, 72 
External respiration, 39 
Eyes of arthropoda, 175, 183; 

of mollusca, 159; of vermes, 
171; of vertebrata, 111, 116 
Eyespot, 150 



Faecal matter, 59 

False feet, 176 

Fat, 57, 76 

Fats, 52, 53, 56, 57, 58, 81 

Female, 91 

Fermentation, 64 

Ferments (see Enzyme) 

Fertilization, 89, 91, 96, 133 

Fever, 83 

Fibrin, 80 

Finger, 108, 109 

Fish, 185, 188 

Fission, 89, 132, 143, 171, 190 

Flat worms, 170 

Flower, 96, 97 

Fly, 173, 184 

Food, 11, 12, 21, 45, 46, 116 

Food substances, 51, 53, 75, 76, 

129, 185 
Foods, 54 

Foot, 108, 155, 157 
Forearm, 109 
Fresh air, 44 
Frog, 188 
Function, 1, 2 
Functions, 3, 21 

Ganglia, 116, 159, 169, 173, 180 

Gas, 13, 14, 16, 17, 19, 22, 24, 
25, 27, 29, 32, 43 

Gastric juice, 56 

Gastrula, 47, 92, 93 

Generations, alternation of, 
145, 146, 190 

Germ layers (see Primary lay- 
ers) 

Germs (see Disease germs) 

Gillbailer, 180 

Gills, structure of, 31, 32; of 
echinodermata, 151; of mol- 
lusca, 157; of arthropoda, 
174; of lobsters, 180; of 
acerata, 181; of vertebrata, 
186 

Girdle, 163, 170 

Gizzard, 166 

Glands, 50 

Grasshopper, 184 

Green glands, 174, 179 

Growth, 10 

Gullet, 129 



208 



INDEX 



Hair, 7, 8 

Hair cell, 8 

Hand, 108 

Head, 173, 176, 181, 182 

Health, 44 

Hearing, 183 

Heart, 68, 69, 70, 85, 157, 158, 

175, 179, 187 
Heart beat, 70, 74 
Heart muscle, 69, 118 
Heart strain, 84, 85 
Heat, 13, 14, 18, 21, 46, 53, 80, 

82, 83 
Heat, sensation of, 83 
Hemoglobin, 77, 78 
Herbivorous animals, 51 
Hepatic glands, 150 
Hermaphroditic organisms, 170, 

175 
Hexapoda, 182 
Hinge joints, 109, 110, 178 
Hip bone, 106 
Hoofs, 187 

Hydra, 136, 137, 139 
Hydroid, 138, 140, 142, 145, 

146 
Hydrocarbons (see Fats), 52, 

53 
Hydrogen, 17, 52, 53 
Hygiene, 62 
Hypostome, 139 

Impulse, nervous, 113 
Indigestion, 64, 65 
Influence of pressure, 25 
Ink, 159 

Insects, 103, 182, 184, 
Inspiration, 38, 39, 42, 72 
Internal respiration, 39 
Intestine, 50, 58, 164, 186 
Involuntary muscle, 100, 101 
Iodine, 12 

Irritability, 99-120; of proto- 
zoa, 9, 10, 11, 128; of coelen- 
terata, 141; of starfish, 150; 
of earthworms, 162; of lob- 
sters, 176, 177; of vertebrata, 
185; of plants, 189 

Jaws, 176 

Jellyfish, 137, 138, 140, 141, 
145, 146 



Joints, 104, 109, 110, 178 

Kidneys, 59, 60, 61, 62, 186 

Lacteals, 58, 81 

Lady bugs, 184 

Large intestine, 58 

Larvae, 180, 183, 184 

Law, 21, 44 

Leaf, 13, 16 

Leech, 172 

Leg, 105, 106, 107, 108 

Legs, 182 

Ligament, 104 

Light, 190 

Lime water, 18, 190 

Lines of growth, 155 

Lingual ribbon, 160 

Lipase, 56 

Liquid, 13, 14, 22 

Liver, 57, 58, 76, 150, 152, 159, 

174, 179, 186 
Living matter, 2, 7, 9, 21, 45, 

87 (see characteristics of) 
Lobster, 49, 103, 173, 176 
Locomotion, 126; of protozoa, 

129; of coelenterata, 141, 142; 

of starfish, 150, 151; of clam, 

155; of earthworm, 162, 163; 

of lobster, 176, 177, 180 
Locust, 184 
Lungs, 33, 34, 38, 41, 59, 181, 

186 
Lung membrane, 44, 60 
Lyniph, 81 
Lymph hearts, 81 
Lymphatics, 81 



Magnesium, 17 

Malaria, 128 

Male, 91 

Malpighian tubes, 174, 182 

Maltose, 56 

Mammal, 188 

Many-celled animals, 43, 47, 89, 

99, 125, 135, 143 
Mandibles, 178 
Mantle, 154, 155 
Mantle chamber, 156 
Matter, 13 
Maxilla, 178 



INDEX 



209 



Maxillipeds, 176 

May Hies, 184 
Moat, 54 

Mechanism, 42, 44 
Membrane (see Moist mem- 
brane) 
Mesoderm, 93, 136, 139, 143 
Metamorphosis, 161, 172, 180, 

183, 184 
Microbes, 79 
Milk, 54 

Millipeds, 181, 183 
Mites, 181 
Moist membrane, 13, 15, 16, 24, 

25, 29, 31, 32, 33, 42, 43 
Mollusca, 154-161 
Molluscoidea, 171, 172 
Moulting, 179 
Mosquito, 184 
Mother of pearl, 159 
Motion, 10, 13, 14, 15, 21, 45, 

99 
Moths, 184 

Motor (efferent) nerves, 113 
Mouth, 148 
Mouth parts, 182 
Movements, 10, 99, 110, 111, 

113, 115, 150 
Muscle, 57, 150, 185; cells, 

100; relation to bones, 110, 

111; of respiration, 36, 42; 

structure of, 100, 101, 102, 

114 
Muscular contraction, 99, 100, 

101 
Muscular energy, source of, 46, 

100 
Muscles, work of, 84 
Mussel, 158 
Myriapoda, 181 

Nails, 187 
Narcotic, 118 

Nephridia, 160, 167, 169, 179 
Nerve cell, 112 
Nerve cord, 169, 180, 182 
Nerve fiber, 112 

Nerves, 113, 114, 180, 181, 185 

Nerves, relation to muscles, 111 

Nervous system, 112-117; of 

coelenterata, 143 j of echino- 



dermata, 113, 150; of mol- 
lusca, 158, 159; of vermes, 
113, 169; of arthropoda, 173- 
175, 181; of vertebrata, 187 

Nettle cells, 140 

Nitrogen, 20, 29, 53, 61 

Nitrogenous compounds, 169, 
186 

Noises, 42 

Non-living matter, 11, 87 

Non-sexual reproduction (see 
Fission, Budding) 

Nucleus, 9, 20 

Nutriment, 53, 54 

(Esophagus, 57, 99, 139, 150, 

151 
Oils, 52 
One-celled animals, 9, 10, 11, 

29, 43, 46, 88, 125, 128-134 
Organism, 7, 9, 16, 21 
Osmosis, 15, 16, 22, 32, 58, 60, 

72, 81, 132, 141 
Ovary, 91, 169 
Ova (see Egg-cell) 
Oviduct, 94, 167 
Oxidation, 22, 117 
Oxygen. 16, 17, 18, 19, 20, 23, 

28, 29, 31, 32, 33, 34, 40, 41, 

42, 43, 44, 52, 53. 77, 78, 92, 

117, 132, 141, 151, 157, 160, 

174, 180, 186, 190 
Oxvhemoglobin, 77 
Oysters, 103, 159 

Pancreas, 186 

Pancreatic juice, 56, 58 

Paramecium, 10, 88, 130 

Parasites, 171 

Parthenogenesis, 176 

Particles, 13, 14, 15, 16, 24, 43 

Pearl oyster, 159 

Pelvic girdle, 105 

Pepsin, 56 

Peptones, 56, 08 

Peristaltic action, 54, 57, 102, 

179 
Perspiration, 61, 62, 83 
Phosphorus, 53 
Physics, 2, 3 



210 



INDEX 



Physiological properties of pro- 
toplasm (see Living matter) 

Physiology, 1, 2, 7, 124 

Pisces, 188 

Plants, 1, 2, 9, 19, 52, 53, 95, 
125, 189-191 

Plasma, 80 

Poisonous substances, 58, 79, 
140 

Poison jaws, 181 

Pores of skin, 61 

Potato, 12, 16, 19 

Potato section, 12 

Pressure, 24, 25, 26, 27, 28, 29, 
30, 31, 32. 34, 38, 39, 43, 78, 
85, 142, 151, 186 

Primary layers, 93, 135, 136 

Proteids, 53, 56, 57, 61, 75, 76, 
80 

Protoplasm, 8, 9, 10, 11, 12, 21, 
53, 87, 124 

Protozoa, 128 

Pulmonary artery, 72, 73 

Pulmonary vein, 72, 73 

Pulse, 74 

Radial canal, 151 

Radial nerve, 150 

Radial symmetry, 148, 149, 152 

Rate of heart beat, 85; of res- 
piration, 85; of passage of 
gas, 25, 26 

Red blood corpuscles, 76, 77, 78 

Reflex action, 114 

Regeneration, 152, 153 

Relaxation, 42 

Reproduction, 87-98; of proto- 
zoa, 11, 132; of coelenterata, 
143-145; of echinodermata, 
152; of mollusca, 161; of 
earthworms, 169, 170; of 
vermes, 171, 172; of arthrop- 
oda, 175, 176, 180, 183; of 
vertebrata, 188 

Reproductive cells, 89, 90, 144, 
190 

Reproductive organs, 90, 180, 
186 

Reptilia, 188 

Respiration, 23-44; of protozoa, 
132; of coelenterata, 141; of 



echinodermata, 151; of mol- 
lusca, 156, 157, 160; of 
vermes, 164; of arthropoda, 
174, 175, 180, 183; of ver- 
tebrata, 186 

Retractor muscles, 152 

Rhythmical contraction of 
heart, 69, 70, 85; in in- 
sects, 183; of jellyfish, 141; 
of muscles, 101, 102 

Ribs, 36, 37, 105, 106, 107 

Roots, 13, 16 

Round worms, 171 

Rust, 18 

Saliva, 56 

Salt, 52 

Salts, 52 

Sap, 19, 20 

Scales, 187 

Scallops, 159 

Science, 123 

Scorpions, 181 

Sea anemone, 102, 137, 139, 

140, 141, 143 
Sea urchin, 90 
Segment, 168, 173, 181 
Segmentation, of animals, 171, 

173, 180, 181, 187; of egg 

(see Cell division) 
Segmented animals, 169 
Segmented worms, 172 
Seminal receptacles, 169 
Seminal vesicles, 166, 167 
Sensations, 83, 84, 113 
Sense organs, 115, 143, 150, 

159, 175, 176, 178, 182, 187 
Senses, special, 115 
Sensory (afferent) nerves, 113 
Sepia, 159 
Septa, 168 
Serum, 80 
Setae, 163 
Sexual cells, 91 
Sexual reproduction, 88-94 
Shells, 154, 155, 156 
Shivering, 117 
Shoulder blade, 105 
Shoulder girdle, 105 
Shrimp, 176 
Sight, sense of, 175 



INDEX 



211 



Silver fish, 184 

Sinus, 157, 178, 179 

Siphon, 157, 1(31 

Skeleton of man, 103-109; of 
corals, 143; of echinoderms, 
147, 148; of mollusca, 154; 
of arthropoda, 173; of verte- 
brata, 185, 187 

Skin, 64 

Smell, sense of, 115, 116, 175 

Snakes, 188 

Sodium chloride, 52, 75, 101 

Soft shell crab, 179 

Soil, 164 

Solid, .13, 18, 22, 60 

Spaces, 14, 15, 16, 24, 43 

Speech, 42 

Sperm cell, 91, 96, 145, 152, 169 

Sperm duct, 94, 167 

Sperm nucleus, 91 

Spermarv, 91, 170 

Spider, 173, 181 

Spinal column, 104, 105, 185 

Spinal cord, 112, 113, 114, 169 

Spinal nerve, 113, 116 

Spinnerets, 181 

Squid, 159, 160, 161 

Starch, 12, 13, 16, 18, 19, 52, 
53, 56*, 57, 58, 190 

Starfish, 49, 66, 103, 112, 148, 
149, 150, 151, 152 

Starvation, 76 

Sternum (breast bone), 105 

Stimulants, 54 

Stimulus, 101, 113, 114 

Stomach, 49, 50, 57, 116, 150, 
182 

Stone canal, 151 

Storage of food, 19, 76 

Structure, 1, 3, 126, 127 

Sucker, 151 

Suction, 141 

Sugar, 19, 20, 52, 56, 58, 76 

Sulphur, 53 

Summary of chapters, living 
matter, 20, 22; respiration, 
42-44; assimilation, 65; cir- 
culation, 85, 86; reproduc- 
tion, 97; irritability, 119, 
120 •„ protozoa, 133, 134; 
coelenterata, 146; echinoder- 



mata, 153; mollusca, 160; 

vertebrata, 187 
Swallowing, 57 
Sweat glands, 59, 61, 64, 83, 

117 
Swimmerets, 180 
Symmetry, bilateral, 149, 152, 

155; serial, 163; radial, 148, 

149, 152 
Sympathetic system, 116 

Tape worm, 171 

Tactile organs, 176 

Tactile sense, 162, 175 

Taste, sense of, 115, 116, 175, 
183 

Tea, 54 

Teeth, 64 

Temperature, regulation of 
body, 82, 83, 84 

Tendon, 101 

Tentacles, 140 

Testis (see spermary), 167 

Test for starch, 12 

Theory of muscular contrac- 
tion, 100 

Thirst, 65 

Thoracic duct, 73, 81 

Thorax, 173, 176, 181, 182 

Ticks, 181 

Tissues, 135, 136 

Tone, 74, 75, 82, 83 

Tongue, 57 

Touch, sense of, 115 

Trachea (windpipe), 35 

Tracheae, 174, 181, 183 

Trichina, 171 

Tube feet, 148, 150, 151, 152 

Tuberculosis, 41 

Turtles, 188 

Typhlosole, 164, 168 

Undifferentiated cells, 89 
Unfertilized eggs, 176 
Upper arm, 109 
Urea, 60, 61, 132 
Ureter, 61 

Vacuole, 9 

Valves, 70, 71, 81, 154 

Vasomotor nerves, 81, 82 



212 



INDEX 



Vegetables, 54 

Veins, 71, 72, 81 

Venous system, 73 

Ventilation, 44 

Ventricles, 69, 70, 72, 74, 157 

Vermes, 162-172 

Vertebrae, 105 

Vertebral column (see Spinal 

column ) 
Vertebrata, 184-188 
Vibrations, 13, 143, 159, 162, 

175, 178 
Villi, 58, 59 
Voice, 42 

Voluntary muscle, 100 
Vorticella, 10, 133 

Wandering jew, 7 



Warm-blooded animals, 188 

Wasp, 184 

Waste products, 46, 59, 81, 131, 

160 
Water, 13, 14, 15, 16, 17, 18, 

20, 22, 29, 31, 32, 33, 43, 51, 

52, 55, 60, 61, 65, 190 
Water- vascular system, 150, 

151 
Web, 181 

Weight of air, 20 
White blood corpuscles, 76, 77, 

78, 79 
Wings, 182, 183 
Windpipe (see Trachea) 
Wood, 17 

Work, muscular, 53 
Worms (see Vermes) 



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